Abstract:
The invention relates to an injector for injecting fuel into a combustion chamber of an internal combustion engine. The injector is actuated by an actuator and is connected to a fuel supply line via which fuel is supplied under system pressure. At least one injection opening can be opened or closed off by an injection valve member, which is activated by a control piston via a control chamber to which the control piston and a piston section of the injection valve member are exposed with respective pressure faces. The control piston is a valve piston of a control valve. The pressure face of the control piston and the pressure face of the piston section of the injection valve member are exposed to the control chamber at the same side. The control piston and the piston section of the injection valve member also enclose a further control chamber which is connected to a fuel return line when the control valve is open and to the fuel supply line when the control valve is closed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2007/055939 filed on Jun. 15, 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is based on an injector for injecting fuel into a combustion chamber of an internal combustion engine. 
     2. Description of the Prior Art 
     From German Patent Disclosure DE-A 10 2004 015 744, a fuel injector for injecting fuel into a combustion chamber of an internal combustion engine is known, which has an injector housing that has a fuel inlet which is in communication with a central high-pressure fuel source outside the injector housing and with a pressure chamber inside the injector housing, from which fuel subjected to high pressure is injected as a function of the position of a control valve. The control valve is actuated by means of a piezoelectric actuator. To attain a sufficiently long stroke length for the control valve, a coupling chamber is embodied between the control valve and the piezoelectric actuator. This chamber acts as a hydraulic booster on the valve piston of the control valve. 
     It is the disadvantage of the fuel injectors known from the prior art, which are actuated by a piezoelectric actuator, that the piezoelectric actuator must be very long in order to attain a sufficiently long travel of the valve piston of the control valve. This leads to a long structural length of the fuel injector. 
     ADVANTAGES AND SUMMARY OF TILE INVENTION 
     An injector embodied according to the invention for injecting fuel into a combustion chamber of an internal combustion engine is actuated by means of an actuator and communicates with a fuel inlet by way of which fuel at system pressure is delivered. In the injector, at least one injection opening can be opened or closed by an injection valve member, and the injection valve member is triggered by means of a control piston via a control chamber, to which the control piston and a piston portion of the injection valve member are exposed by their respective pressure faces. The control piston is at the same time a valve piston of a control valve. The valve piston and the piston portion of the injection valve member surround a further control chamber, which when the control valve is open communicates with a fuel return and when the control valve is closed communicates with the fuel inlet. In a first opening phase of the injection valve member, the control piston acts on the injection valve member via the first control chamber, on the principle of direct triggering. A further opening phase of the injection valve member ensues when the control piston acts as a valve piston of a servo valve and triggers the further control chamber. The essence of the invention resides in a combination of direct triggering and servo triggering of the injection valve member; the opening of the injection valve member is effected when the actuator moves the control piston in the direction of the injection openings. The advantage of the injector embodied according to the invention is that as a result of the design of the control piston as a valve piston for the control valve, no additional control valve has to be embodied in the injector to make the operation of the injector possible. For this reason, the structural size of the injector can be reduced. A further advantage of the injector embodied according to the invention is that the stroke of the actuator is boosted in such a way that even a short actuator suffices to generate a sufficiently long stroke of the injection valve member. As a result, it is possible to reduce the structural height of the injector. Furthermore, by the embodiment according to the invention of the injector, the opening speed of the injection valve member at the onset of the opening event is increased, compared to the fuel injectors known from the prior art. 
     So that the valve piston and the injection valve member will surround the further control chamber, in a first embodiment, an annular portion is embodied on the control piston, and the piston portion of the injection valve member is guided in it. The further control chamber is defined by the injection valve member and the annular portion. 
     In a second embodiment, the annular portion is embodied on the piston portion of the injection valve member. The control piston is guided in the annular portion, and the further control chamber is defined by the control piston and the annular portion. 
     To increase the stroke of the control piston still further compared to the actuator stroke, in a further embodiment the actuator is connected to a booster piston, and the booster piston, with an end face, defines a booster chamber, which is defined on the diametrically opposite side by an upper end face of the control piston. The ratio of the strokes of the booster piston and the control piston is proportional to the ratio of the diameters. The greater the diameter of the booster piston compared to the diameter of the end face, defining the control chamber, of the control piston, the longer the stroke of the control piston compared to the stroke of the booster piston. 
     To enable a sufficiently long stroke of the injection valve member and thus to enable injecting a sufficiently large quantity of fuel into the combustion chamber of the engine, the control chamber that is defined by the injection valve member and the control piston communicates, through a connecting conduit, with a valve chamber that surrounds the control piston. The valve chamber is a valve chamber of the control valve. As soon as the control valve opens, the valve chamber that surrounds the control piston is in communication with a fuel return. As a result, the further control chamber is pressure-relieved when the control valve is open. The injection valve member can travel a longer distance. 
     In a preferred embodiment, in the connecting conduit, through which the control chamber, which is defined by the injection valve member and the control piston, communicates with the valve chamber, a throttle element is received. By means of the throttle element, the pressure relief and pressure loading of the control chamber are damped. This prevents a return kick on the part of the injection valve member. Moreover, the throttle element acts as a tolerance limiter in the connecting conduit. 
     To enable filling the further control chamber with fuel at system pressure when the control valve is closed, the valve chamber of the control valve, which chamber communicates with the further control chamber via the connecting conduit, communicates with the fuel inlet by means of a throttle element. 
     In an embodiment of the fuel injector in which the injection valve member is guided in an annular portion in the control piston, a lower end face on the annular portion defines the control piston, and a shoulder on the piston portion of the injection valve member defines the control chamber. As a result, upon a motion of the control piston into the control chamber, the injection valve member is pushed out of the control chamber. This embodiment has the effect that when current is supplied to the actuator, or in other words the actuator has expanded, the control piston is moved into the control chamber, and as a result of this motion of the control piston the injection valve member moves out of the control chamber and thus lifts from its seat and opens the at least one injection opening. By the ratio of the size of the end face on the annular portion of the control piston to the area of the shoulder that defines the control chamber, the stroke of the injection valve member can be adjusted as a function of the stroke of the control piston. The smaller the area of the shoulder compared to the area of the end face on the annular portion of the control piston, the longer the stroke of the injection valve member in comparison to the stroke of the control piston. 
     In a further embodiment of the fuel injector, in which the piston portion of the injection valve member has an annular portion in which the control piston is guided, an end face on the annular portion of the piston portion of the injection valve member and a shoulder on the control piston define the control chamber. The function is the same as in the embodiment in which the annular portion is embodied on the control piston, and an injection valve member is guided in that annular portion on the control piston. Here as well, the boosting of the motion of the injection valve member in comparison to the control piston is dependent on the cross-sectional area of the end face of the piston portion of the injection valve member and on the surface area of the shoulder that defines the control chamber. Here as well, the boosting of the motion of the injection valve member in comparison to the control piston is dependent on the cross-sectional area of the end face of the piston portion of the injection valve member and on the surface area of the shoulder that defines the control chamber. 
     To enable actuating a control piston with the aid of the actuator, preferably a piezoelectric actuator, the control piston in one embodiment is connected directly to the actuator. 
     To compensate for differences in stroke that can occur from the thermal expansion of the actuator, the actuator is preferably received in a housing that is made of a material whose coefficient of thermal expansion is equivalent to that of the actuator. Because of the virtually identical coefficients of thermal expansion, the housing in which the actuator is received is preferably made of Invar, if the actuator is a piezoelectric actuator. 
     To compensate for any residual error in the coefficient of thermal expansion that may occur between the actuator and the housing, in a preferred embodiment a compensating element is received between the actuator and the housing. The compensating element is made from aluminum or aluminum alloys, for instance. 
     The embodiment in which the housing is made from a material whose coefficient of thermal expansion is equivalent to that of the actuator, and in which between the housing and the actuator a compensating element is received by which a residual error of the coefficient of thermal expansion between the actuator and the housing is compensated for, is especially preferable whenever the control piston is connected directly to the actuator. This is necessary in order to assure a clean closure of the control valve. Any residual error that may occur in the stroke for generating the tightness of the control valve can be compensated for electrically, for example. For that purpose, it is possible to operate the actuator in bipolar fashion, for example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are shown in the drawings and described in further detail in the ensuing description, in which: 
         FIG. 1  shows a fuel injector embodied according to the invention, in a first embodiment; 
         FIG. 2  shows a fuel injector embodied according to the invention, in a second embodiment; and 
         FIG. 3  shows a fuel injector embodied according to the invention, in a third embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , a fuel injector embodied according to the invention is shown in a first embodiment. 
     A fuel injector  1  includes an injection valve member  3 , which is guided in a guide  5  in a lower housing part  7 . A sealing edge  9  is embodied on the injection valve member  3  and when the injection opening  11  is closed is located in a seat  13 . In addition to the embodiment shown here, in which the fuel injector  1  has one injection opening  11 , it is also possible for more than one injection opening  11  to be provided. 
     The injection valve member  3  is surrounded by a nozzle chamber  15 . The nozzle chamber  15  communicates via an inflow conduit  17  with a fuel inlet  19 . The fuel inlet  19  communicates in turn with a high-pressure reservoir, not shown here, of a common rail system. 
     On its end remote from the injection opening  11 , the injection valve member  3  has a piston portion, which is guided in an annular portion  21  of a control piston  23 . An end face  57 , which as a pressure face is exposed to a control chamber  59 , is embodied on the annular portion  21 . A shoulder  61  is embodied on the piston portion of the injection valve member  3 ; as a further pressure face, it likewise defines the control chamber  59 , on the same side as the end face  57  of the annular portion  21 . As a result, the injection valve member  3 , upon a motion of the control piston  23 , is moved in the opposite direction, so that a stroke reversal of the actuator stroke occurs, relative to the stroke of the injection valve member  3 . By means of the annular portion  21  and an upper end face  25  of the injection valve member  3 , a further control chamber  27  is enclosed. A spring element  29 , which is preferably a spiral spring embodied as a compression spring, is received in the further control chamber  27 . 
     The control piston  23  simultaneously functions as a valve piston of a control valve  31 . To that end, a sealing edge  33  is embodied on the control piston  23 . When the control valve  31  is closed, the sealing edge  33  is located in a seat  35  of the control valve  31 . On the side toward the injection valve member  3 , the control piston  23  is surrounded by a valve chamber  37 . 
     In the annular portion  21  of the control piston  23 , a connecting conduit  39  is embodied, through which the valve chamber  37  communicates with the further control chamber  27 . A throttle element  41  also discharges into the valve chamber  37  and causes the valve chamber  37  to communicate with the inflow conduit  17 . As a result, when the control valve  31  is closed, the control chamber  27  is filled with fuel at system pressure, via the throttle element  41 , the valve chamber  37 , and the connecting conduit  39 . 
     A platelike portion  43  is embodied on the control piston  23  and is connected to an actuator  45 , preferably to a piezoelectric actuator. Instead of a piezoelectric actuator, any other actuator known to one skilled in the art can be used that expands on being supplied with current and contracts upon determination of the supply of current. 
     On the side diametrically opposite the control piston  23 , the actuator is connected to a disk  47 . To achieve the necessary prestressing, the actuator is surrounded by a spring element  49 . The spring element  49  is preferably a tubular spring embodied as a tension spring. 
     To avoid malfunctions that can occur from the thermal expansion of the actuator  45 , the actuator  45  is received in a housing  51  that is made of a material that has essentially the same coefficient of thermal expansion as the actuator  45 . If the actuator  45  is a piezoelectric actuator, then the housing  51  is preferably made from Invar. To compensate for any residual error that may occur because of the different coefficients of thermal expansion, in the embodiment shown in  FIG. 1  a compensating element  53  is received between the disk  47 , which is connected to the actuator  45 , and the housing  51 . The compensating element  53  is made from aluminum, for example. 
     By means of the housing  51 , an actuator chamber  55  is embodied, which in operation of the fuel injector  1  is filled with fuel. As a result, the actuator  45  is bathed by fuel. Because of the good thermal conductivity of the fuel, the heat that is generated by the actuator  45  in operation is transmitted to the housing  51 . Thus the fuel with which the actuator  45  is bathed simultaneously serves to cool the actuator  45 . 
     To start the injection event, current is supplied to the actuator  45 . As a result, the actuator  45  expands. As a result of the expansion of the actuator  45 , the control piston  23  is moved in the direction of the injection valve member  3 . As a result of the motion of the control piston  23 , the pressure in the control chamber  59  increases. The thus-increasing pressure force acts on the shoulder  61  on the piston portion of the injection valve member  3  and moves the injection valve member  3  in the opposite direction to the actuator stroke and lifts the injection valve member  3  from its seat  13  and as a result opens the at least one injection opening  11 . In this opening phase of the injection valve member  3 , the control piston  23  acts directly on the injection valve member  3  via the control chamber  59 . At the same time, by the motion of the control piston  23 , the sealing edge  33  of the control valve  31  lifts from its seat  35  and thus opens a communication from the valve chamber  37  into a fuel return  63 . As a result, the pressure in the valve chamber  37  drops to the return pressure. Because of the lowered pressure in the valve chamber  37 , fuel flows from out of the further control chamber  27  via the connecting conduit  39  into the valve chamber  37  and from there onward into the fuel return  63 . The pressure in the further control chamber  27  decreases. In this further opening phase of the injection valve member  3 , the control piston  23  acts as a valve piston of a servo valve and triggers the further control chamber  27 . Because of the decreasing pressure in the control chamber  27 , the motion of the injection valve member  3  is made easier. Fast opening of the injection valve member  3  with a boosted actuator stroke is thus achieved. 
     To terminate the injection event again, the supply of current to the actuator  45  is stopped. The actuator  45  contracts and as a result moves the control piston  23  in the direction of the actuator  45 . As a result of this motion, the end face  57  lifts out of the control chamber  59  and thus increases the volume of that chamber. The pressure in the control chamber  59  decreases. As a result, a lesser pressure force acts on the shoulders  61  at the injection valve member  3 . As soon as the pressure force which acts on the shoulders  61  of the injection valve member  3  is less than the pressure force that acts on the upper end face  25  of the injection valve member  3 , the injection valve member  3  moves into its seat  13  and thereby closes the injection opening  11 . The motion of the injection valve member  3  is supported by the fact that by the motion of the control piston  23 , the sealing edge  33  is put into its seat  35 , and thus the control valve  31  is closed. As soon as the control valve  31  is closed, fuel at system pressure can flow out of the inflow conduit  17  into the further control chamber  27 , via the throttle element  41 , the valve chamber  37 , and the connecting conduit  39 . The pressure in the further control chamber  27  rises to system pressure. As a result, a further-increased pressure force is exerted on the upper end face  25  of the injection valve member  3 . The motion of the injection valve member  3  is accelerated. 
     So that the control valve  31  will close tightly, so that no fuel can flow out of the valve chamber  37  into the fuel return  63  when the control valve  31  is closed, it is necessary that any changes in length of the actuator that occur as a result of increasing temperature be compensated for. This is done first by making the housing  51  from a material which has approximately the same coefficient of thermal expansion as the actuator  45 . Differences in the coefficients of thermal expansion of the actuator  45  and the housing  51  are compensated for by the compensating element  53 , for example. Should a residual error in the stroke nevertheless occur, causing the control valve  31  not to close tightly, it is possible to compensate for this error electrically. For that purpose, the actuator is for instance operated in bipolar fashion. However, that requires the use of a bipolar piezoelectric actuator. The advantage of the bipolar piezoelectric actuator is that when the voltage reverses it contracts. It is thus possible, if the control valve  31  does not close because of the thermal expansion of the actuator  45 , to apply a negative voltage to the actuator  45  and thus bring about a contraction of the actuator  45 . As a result, the control piston  23  is moved farther in the direction of the actuator  45 , and the sealing edge  33  is put into its seat  35 . 
     In  FIG. 2 , a fuel injector embodied according to the invention is shown in a second embodiment. 
     The fuel injector shown in  FIG. 2  differs from the fuel injector shown in  FIG. 1  in that the control piston  23  is not connected to the actuator  45 , but instead, with an upper end face  65 , defines a booster chamber  67 . On the side diametrically opposite the upper end face  65 , the booster chamber  67  is defined by an end face  69  of a booster piston  71 . A platelike extension  73 , which is connected to the actuator  45 , is embodied on the booster piston  71 . 
     Since the control piston  23  is not connected directly to the actuator  45  and instead, a hydraulic transmission of the motion of the actuator  45  to the control piston  23  is effected, in the embodiment shown in  FIG. 2 , there is no need to compensate for a stroke error caused by thermal expansion by providing a housing  51  made of material whose coefficient of thermal expansion is equivalent to that of the actuator  45 . Compensating for the stroke error is done by means of the booster chamber  67 . Simultaneously, by means of the booster chamber  67 , it is possible to boost the stroke of the actuator  45  to the stroke of the control piston  23 . The boosting ratio is dependent on the diameter d 1  of the booster piston  71  and the diameter d 2  of the control piston  23 . As soon as the diameter d 1  of the booster piston  71  is greater than the diameter d 2  of the upper end face  65  of the control piston  23 , the stroke of the control piston  23  is longer than the stroke of the booster piston  71 . As a result, it is possible to reduce the structural height of the actuator  45 , since only a shorter stroke of the actuator  45  is required. 
     The operation of the fuel injector having the embodiment shown in  FIG. 2  differs from the embodiment shown in  FIG. 1  in that when current is supplied to the actuator  45 , the actuator  45  expands, and as a result, the booster piston  71  is moved with the end face  69  into the booster chamber  67 . As a result, the volume in the booster chamber  67  decreases. The pressure in the booster chamber  67  increases. Because of the increasing pressure, an increased pressure force is exerted on the upper end face  65  of the control piston  23 . Because of this increased pressure force on the upper end face  65  of the control piston  23 , the control piston  23  is moved in the direction of the injection valve member  3 . As a result of the motion of the control piston  23 , the sealing edge  33  is lifted from its seat  35 , and the control valve  31  opens. Simultaneously, the end face  57  of the annular portion  21  is moved into the control chamber  59 , and as a result the volume in the second control chamber  59  decreases and accordingly a greater pressure force is exerted on the shoulders  61  on the injection valve member  3 . The injection valve member  3  is lifted from its seat. As a result of the opening of the control valve, the pressure in the further control chamber  27  is reduced, since fuel can flow from the control chamber  27  into the fuel return  63 , via the connecting conduit  39  and the valve chamber  37 . Because of the decreasing pressure in the control chamber  27 , rapid opening of the injection valve member  3  and thus rapid opening of the at least one injection opening  11  are possible. 
     To terminate an injection event, the supply of current to the actuator  45  is withdrawn. The actuator  45  contracts. As a result, the booster piston  71  is moved with the end face  69  out of the booster chamber  67 . The volume in the booster chamber  67  increases. As a result, the pressure in the booster chamber  67  decreases, and a lesser pressure force acts on the upper end face  65  of the control piston  23 . As a result, the control piston  23  is moved into the booster chamber  67 , in the direction of the booster piston  71 . This motion of the control piston  23  causes the sealing edge  33  to be put into the seat  35 , and thus the control valve  31  closes off the communication from the valve chamber  37  into the fuel return  63 . At the same time, by the motion of the control piston  23 , the end face  57  of the annular portion  21  is lifted out of the second control chamber  59 , and thus the volume in the control chamber  59  increases. As a result, the pressure force that is exerted on the shoulders  61  of the injection valve member  3  decreases. Since because of the closed control valve  31  fuel at system pressure flows into the further control chamber  27 , via the internal throttle restriction  41 , the valve chamber  37 , and the connecting conduit  39 , and since as a result the pressure in the further control chamber  27  increases, an increased pressure force acts on the upper end face  25  of the injection valve member  3 . The injection valve member  3  is put with the sealing edge into its seat  13  and thus closes the at least one injection opening  11 . The injection event is ended. As a result of the pressure buildup in the further control chamber  27 , the closing motion of the injection valve member  3  is increased. 
       FIG. 3  shows a fuel injector embodied according to the invention in a third embodiment. 
     Unlike the fuel injector shown in  FIG. 2 , in the fuel injector shown in  FIG. 3 , an annular portion  75  is embodied on the piston portion of the injection valve member  3 , in which annular portion the control piston  23  is guided. The annular portion  75  and the control piston  23  surround the further control chamber  27 . With an end face  77 , the annular portion  75  on the piston portion of the injection valve member  3  defines a control chamber  79 . A shoulder  81  is also embodied on the control piston  23 ; it defines the control chamber  79  on the same side as the end face  77  of the annular portion  75 . Relative to a third control chamber  83 , which communicates with the fuel inlet  19  via the inflow conduit  17 , the second control chamber  79  is defined by a ring element  85 , which surrounds the annular portion  75  on the injection valve member  3 . For that purpose, the ring element  85  is placed with a biting edge  87  against a shoulder  89  on the middle housing part  91 . The force required for this is exerted by a spring element  93 , which is braced on one end against the ring element  85  and on the other against the lower housing part  7 . The spring element  93  is preferably a spiral spring embodied as a compression spring. 
     To damp pressure fluctuations that may occur in the control chamber  27 , a throttle element  95  is embodied in the connecting conduit  39 . 
     Besides the embodiment shown in  FIG. 3 , in the embodiments shown in  FIGS. 1 and 2  it is also possible to provide a throttle element in the connecting conduit  39  by which the further control chamber  27  communicates with the valve chamber  37 . 
     So that fuel at system pressure can flow out of the third control chamber  83  into the nozzle chamber  15 , in the embodiment shown in  FIG. 3  at least one flat face  97  is embodied in the region&#39;of the guide  5  on the injection valve member  3 . The fuel at system pressure can then flow from the fuel inlet  19  via the inflow conduit  17  into the third control chamber  83  first and from there along the flat face  97  into the nozzle chamber  15 . 
     To start the injection event, in the fuel injector shown in  FIG. 3  as well, the actuator  45  is supplied with current. As a result, the actuator  45  expands. The booster piston  71  connected to the actuator  45  is moved in the direction of the booster chamber  67 . As a result, the volume in the booster chamber  67  decreases. The pressure in the booster chamber  67  rises. Thus an increased pressure force acts on the upper end face  65  of the control piston  23 . The control piston  23  is moved in the direction of the injection valve member  3 . As a result of the motion of the control piston  23 , the sealing edge  33  lifts from its seat  35 . A communication from the further control chamber  27 , via the connecting conduit  39  and the throttle element  95 , to the valve chamber  37  and from there into the fuel return  63 , is opened. The pressure in the further control chamber  27  decreases. Simultaneously, by the motion of the control piston  23 , the volume in the control chamber  79  is increased, since the shoulder  81  is moved in the direction of the injection valve member. As a result, the pressure in the control chamber  79  decreases. A lesser pressure force acts on the end face  77  of the annular portion  75  on the piston portion of the injection valve member  3 . As a result of the pressure force in the third control chamber  83 , which acts on a second shoulder  99  on the injection valve member  3 , the injection valve member is lifted from its seat  13  and opens the at least one injection opening. 
     To terminate the injection event, the supply of current to the actuator  45  is stopped again. The actuator  45  contracts. As a result, the booster piston  71  is moved in the direction of the actuator  45 . This causes the volume in the booster chamber  67  to increase. A lesser pressure force acts on the upper end face  65  of the control piston  23 , and as a result, the control piston  23  is moved in the direction of the booster chamber  67 . The sealing edge  33  is returned to its seat  35  and thus closes the control valve  31 . Via the internal throttle restriction, fuel at system pressure flows out of the inflow conduit into the valve chamber  37  and from there, via the throttle element  95  and the connecting conduit  39 , into the further control chamber  27 . The pressure in the control chamber  27  rises. Simultaneously, by the motion of the control piston  23 , the shoulder  81  on the control piston  23  moves into the control chamber  79 . The volume in the control chamber  79  decreases. As a result, an increased pressure force acts on the end face  77  on the annular portion  75  of the piston portion of the injection valve member  3 . As a result of the pressure forces acting on the injection valve member  3 , this valve member is moved in the direction of the injection opening, until with the sealing edge  9  it is in the seat  13 . The injection opening  11  is closed, and the injection event is ended. 
     In the embodiment shown in  FIG. 3 , the actuator chamber  55  communicates with the inflow conduit  17  via a conduit  101 . As a result, fuel at system pressure is located in the actuator chamber  55 . This fuel serves to dissipate the heat, which occurs in the operation of the actuator, to the housing, since the heat transfer coefficient of the fuel is substantially greater than the heat transfer coefficient of a gas. 
     The foregoing relates to the preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.