Abstract:
An injection nozzle for an internal combustion engine, having a first nozzle needle for controlling the fuel injection through a first injection port, a second nozzle needle for controlling the fuel injection through a second injection port, a first control chamber in which a first control face drive-coupled to the second nozzle needle for introducing closing forces is disposed, and a control line for controlling the pressure in the first control chamber. Especially exact instants of the end of injection can be attained if in the first control chamber, a second control face is disposed that is drive-coupled to the first nozzle needle; a first coupling path connects the first control chamber directly or indirectly to a pressure source; a second coupling path connects the first control chamber directly or indirectly to the pressure source; and the second coupling path is controlled as a function of the stroke of the first nozzle needle such that it is blocked beyond a prestroke of the first nozzle needle.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     2. Field of the Invention  
         [0002]     The invention relates to an improved fuel injection nozzle for an internal combustion engine.  
         [0003]     2. Description of the Prior Art  
         [0004]     One injection nozzle known for instance from German Patent Disclosure DE 100 58 153 A1 has a needle body which has at least one first injection port and at least one second injection port and includes both a first nozzle needle and a second nozzle needle. The first nozzle needle is embodied as a hollow needle, and the second nozzle needle is disposed coaxially to and in the first nozzle needle. With the aid of the first nozzle needle, the injection of fuel through the at least one first injection port can be controlled, while the second nozzle needle serves to control the injection of fuel through the at least one second injection port. The needle body includes a first control chamber, in which a first control face is disposed. This first control face is drive-coupled to the second nozzle needle and is oriented such that a pressure prevailing in the first control chamber generates pressure forces at the first control face that introduce closing forces into the second nozzle needle. Communicating with this first control chamber is a control line, with which the pressure in the first control chamber can be controlled.  
         [0005]     In the known injection nozzle, the needle body furthermore includes a pressure chamber to which a fuel supply line is connected. In this pressure chamber, the first nozzle needle has at least one pressure step, which when the pressure chamber is subjected to pressure introduces opening forces into the first nozzle needle. If a low pressure prevails in the fuel supply line, then closing forces, generated by a suitable closing spring, are generated predominantly at the first nozzle needle. For opening the first nozzle needle, a high pressure is generated in the fuel supply line and, in the first nozzle needle by way of its pressure step, this high pressure generates sufficiently high opening forces. The first nozzle needle is thus directly controlled by the pressure applied to its pressure step so that the first nozzle needle is pressure-controlled.  
         [0006]     The second nozzle needle is likewise equipped with a pressure step, but only when the first nozzle needle is opened is it acted upon by the high pressure and is capable of generating forces operative in the opening direction of the second nozzle needle. As long as a suitable high pressure prevails in the first control chamber, the closing forces predominate in the second nozzle needle. If with the first nozzle needle opened, the pressure in the first control chamber is lowered via the control line, then the opening forces predominate at the second nozzle needle. Thus the second nozzle needle is not controlled directly by the pressure applied to its pressure step but rather indirectly via the pressure in the first control chamber. Accordingly, the second nozzle needle in this case is servo-controlled.  
         [0007]     To enable the second nozzle needle to open quickly, the pressure in the first control chamber drops correspondingly fast. As a result, the second nozzle needle is given a relatively high stroke speed. At certain engine operating points, it is necessary for the injection to be terminated again only briefly after the opening of the second nozzle needle. This can result in configurations in which the second nozzle needle closes too early, for instance if because of its high stroke speed it bounces back from a stop that defines the maximum opening stroke of the second nozzle needle. To attain optimal emissions and power values for the engine, however, it must be possible to predetermine the opening and closing instants of the injection nozzle as exactly as possible.  
       OBJECT AND SUMMARY OF THE INVENTION  
       [0008]     The injection nozzle of the invention has the advantage over the prior art that upon opening of the second nozzle needle, a lesser stroke speed is established for that nozzle needle, so that no bouncing, or only reduced bouncing, of the second nozzle needle occurs. As a result, the end of injection for the fuel injection through the at least one second injection port, or through all the injection ports, can be predetermined with greater accuracy. This is attained by means of the invention in that the first control chamber is connected for communication to a suitable pressure source directly or indirectly via a first coupling path. As a result, the pressure in the control chamber cannot drop so sharply, since hydraulic fluid, in particular fuel, permanently continues to flow in via the first coupling path. It is also of particular significance in the present invention that now both nozzle needles are servo-controlled. For that purpose, a second control face is provided, which is embodied on the first nozzle needle or is drive-coupled to it and which is disposed in the first control chamber, where it can be acted upon by a pressure acting in the closing direction of the first nozzle needle. The pressure in the first control chamber thus controls both the first nozzle needle and the second nozzle needle. A second coupling path has particular significance here; it likewise connects the first control chamber to the pressure source for communication and is controlled as a function of the stroke of the first nozzle needle. The control of the second coupling path is designed such that beginning at the closing position of the first nozzle needle, the second coupling path is open up to a predetermined prestroke of the first nozzle needle and is blocked beyond a stroke of the first nozzle needle that goes beyond the prestroke. As a result of this design, the first control chamber is supplied with replenishing hydraulic fluid upon the opening of the first nozzle needle, until the prestroke is attained, both through the first coupling path and through the second coupling path. Beyond the prestroke, or in other words when the second coupling path is blocked, the supply of hydraulic fluid to the first control chamber is then effected only via the first coupling path. As a consequence, the pressure in the first control chamber, upon opening of the control line that communicates with the first control chamber, initially drops to a first value and then, when the prestroke is reached, drops to a second value that is less than the first. These pressure values can be designed such that at the first pressure value, only the first nozzle needle opens, while at the second pressure value, the second nozzle needle opens as well. The expense for achieving the servo control of the two nozzle needles is comparatively slight as a result. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0009]     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments, taken in conjunction with the sole drawing FIGURE which shows a longitudinal section, greatly simplified, through a basic illustration of a preferred exemplary embodiment of the injection nozzle of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0010]     In  FIG. 1 , an injection nozzle  1  of the invention has a needle body  2 , which protrudes with a nozzle tip  3  into a combustion chamber  4  or a mixture-forming chamber  4  of an internal combustion engine, in particular a Diesel engine. In the region of the nozzle tip  3 , the needle body  2  includes at least one first injection port  5  and at least one second injection port  6 . Typically, a plurality of first injection ports  5  are provided, in particular arranged in a ring. Correspondingly, a plurality of second injection ports  6  may be provided, also expediently arranged in a ring.  
         [0011]     In the needle body  2 , a first nozzle needle  7  is supported with an adjustable stroke. To that end, the needle body  2  includes a first needle guide  8 , which has a first guide cross section  9 . In the closing position shown here, the first nozzle needle  7  is seated in a first seat  10 , which has a first seat cross section  11 . The first nozzle needle  7  is equipped with at least one pressure step  12 , which is oriented toward the injection ports  5 ,  6 . This pressure step  12  is embodied by providing that the first guide cross section  9  is larger than the first seat cross section  11 .  
         [0012]     On the side remote from the first seat  10 , the first nozzle needle  7  is braced on a transmission body  13 , which in this case has a disklike or sleevelike shape. The transmission body  13  is in turn braced, on a side remote from the nozzle needle  7 , on a coupling sleeve  14 . The first nozzle needle  7 , the transmission body  13 , and the coupling sleeve  14  here form a first needle combination  15 , which is supported as a unit, with an adjustable stroke, in the needle body  2 . Since in operation of the injection nozzle  1 , solely pressure forces are transmitted among the individual components of the first needle combination  15 , that is, among the first nozzle needle  7 , the transmission body  13 , and the coupling sleeve  14 , the individual components  7 ,  13 ,  14  of the first needle combination  15  can rest quasi-loosely against one another. It is equally possible for the individual components  7 ,  13 ,  14  to be secured to one another. It is equally possible for at least two of the components, such as the transmission body  13  and the coupling sleeve  14 , to be combined into a one-piece component.  
         [0013]     The first nozzle needle  7  is assigned a restoring spring  16 , by way of which the first needle combination  15  is braced on the needle body  2 . The restoring spring  16  may introduce a restoring force, operative in the closing direction represented by an arrow  17 , which can be introduced into the first nozzle needle  7 . The opening direction is correspondingly represented by an arrow  18 . The restoring spring  16  is braced here on the transmission body  13 , which thus transmits the restoring force to the first nozzle needle  7 .  
         [0014]     The first nozzle needle  7  is embodied as a hollow needle and serves in its interior to support a second nozzle needle  19 , which is coaxial with the first nozzle needle  7 . Accordingly, the first nozzle needle  7  includes a needle guide  20 , which has a second guide cross section  21 . The second nozzle needle  19 , in the closing direction shown here, is seated in a second seat  22 , which is disposed between the at least one first injection port  5  and the at least one second injection port  6  and has a second seat cross section  23 . In the preferred embodiment shown here, it may be expedient also to equip the second nozzle needle  19  with at least one pressure step  24 , which is oriented toward the injection ports  5 ,  6 . Correspondingly, this pressure step  24  is embodied by providing that the second seat cross section  23  is smaller than the second guide cross section  21 .  
         [0015]     On a side remote from the injection ports  5 ,  6 , the second nozzle needle  19  is braced on a transmission bolt  25 , which in turn is braced on a coupling rod  26 . The second nozzle needle  19 , the transmission bolt  25 , and the coupling rod  26  again form a common, adjustable-stroke unit, that is, a second needle combination  27 . If in conventional operation of the injection nozzle  1 , solely pressure forces occur inside the second needle combination  27 , then once again the members of the second needle combination  27 , that is, the second nozzle needle  19 , the transmission bolt  25  and the coupling rod  26 , may rest loosely against one another. Once again, it may be expedient for at least two of the components  19 ,  25 ,  26  to be secured against one another or to be produced as a one-piece component.  
         [0016]     The needle body  2  furthermore includes a first control chamber  28 , in which both a first control face  29  and a second control face  30  are disposed. The first control face  29  is a component of the second needle combination  27  and is embodied here on the coupling rod  26 . In another embodiment, the first control face  29  may also be embodied directly on the second nozzle needle  19 . The first control face  29  is oriented away from the injection ports  5 ,  6 , so that pressure exerted on the first control face  29  transmits a force acting in the closing direction  17  on the second needle combination  27 , which force is thus introduced into the second nozzle needle  19 . In a distinction from this, the second control face  30  is embodied on the first needle combination  15  and is likewise oriented away from the injection ports  5 ,  6 . Accordingly, pressure exerted on the second control face  30  leads to the introduction of a force effected in the closing direction  17  into the first needle combination  15  and thus into the first nozzle needle  7 .  
         [0017]     The first control chamber  28  communicates with a control line  31 , with the aid of which the pressure in the first control chamber  28  can be controlled. In the preferred embodiment shown here, this control line  31  is embodied as an outlet line, and will therefore henceforth be called the outlet line  31 . The outlet line  31  here contains a control valve  32 , which has two connections and two switching positions and can accordingly be embodied on the order of a 2/2-way valve. In the first switching position, shown here, the outlet line  31  is blocked (blocked state). In the other switching position, the outlet line  31  communicates with a return line  33 , which leads to a return  34 , not shown here, which is relatively pressureless and in this sense forms a pressure sink  34  (open state). The return or the pressure sink  34  is for instance a reservoir, and in particular a fuel tank.  
         [0018]     The needle body  2  furthermore includes a second control chamber  35 , which is connected via an inlet line  36  to a pressure source  37 . This pressure source  37  is for instance a high-pressure fuel line, which serves to supply fuel at high pressure to the injection valve  1 . Typically, the high-pressure fuel line  37  supplies a plurality of such injection valves  1  simultaneously with fuel on the so-called common rail principle. This common high-pressure fuel line  37  is then supplied by a common high-pressure fuel pump, not shown. Alternatively, it is equally possible to provide a separate a high-pressure fuel line  37  and/or a separate high-pressure fuel pump for each injection nozzle  1 .  
         [0019]     In the second control chamber  35 , there is a third control face  38 , which is exposed to the pressure prevailing in the second control chamber  35 . The third control face  38  is again oriented away from the injection ports  5 ,  6  and embodied on the first needle combination  15 . The pressure engaging the third control face  38  thus conducts a force, operative in the closing direction  17 , into the first needle combination  15  and hence into the first nozzle needle  7 .  
         [0020]     According to the invention, a first coupling path  39  is now provided, which directly or indirectly connects the control chamber  28  to the pressure source  37  (high-pressure fuel line). In the special embodiment shown here, this first coupling path  39  includes at least one transverse bore  40 , which radially penetrates a cylindrical portion  41  in the first needle combination  15 , in this case the coupling sleeve  14 . The positioning of the transverse bore  40  is selected such that it is open toward the second control chamber  35 . In addition, radially between the first needle combination  15  and the second needle combination  27 , an annular chamber  42  is formed, which is open toward the first control chamber  28  and into which the transverse bore  40  discharges. In this way, a communicating connection is created between the control chambers  28  and  35  through the annular chamber  42  and the transverse bore  40 , and this connection also communicates via the inlet line  36  with the high-pressure fuel line  37 , or in other words the pressure source  37 . It is clear that a plurality of such transverse bores  40  may also be provided, which can be expediently distributed over the circumference on the axial portion  41  of the coupling sleeve  14 . The first coupling path  39  here thus connects the first control chamber  28  directly to the second control chamber  35  and hence indirectly to the pressure source  37 .  
         [0021]     Alternatively, the first coupling path  39  may be formed by a line which connects the first control chamber  28  directly to the pressure source  37  or directly to the inlet line  36  and thus indirectly to the pressure source  37 . This line could then discharge for instance axially into the first control chamber  28 .  
         [0022]     In addition, a second coupling path  43  is provided, which likewise connects the first control chamber  28  directly or indirectly to the pressure source  37  (high-pressure fuel line). In the preferred embodiment shown here, the second coupling path  43  includes at least one longitudinal groove  44 , which is open toward the first control chamber  28  and which, when the first nozzle needle  7  is closed, protrudes into the second control chamber  35 . This longitudinal groove  44  is embodied here in the cylindrical portion  41  of the coupling sleeve  14 . The longitudinal groove  44 , given a suitably shaped first nozzle needle  7 , could also be embodied directly on the first nozzle needle  7 . Alternatively, it is equally possible for the longitudinal groove  44  to be embodied not on the first needle combination  15  but rather on the needle body  2 , specifically in a wall  45  radially defining the first control chamber  28 . In that case, the longitudinal groove  44  would be axially open toward the second control chamber  35  and would be radially open toward the first control chamber  28 . The longitudinal groove  44  has an end  46  remote from the first control chamber  28 . The needle body  2  also has a wall portion  47  which axially defines the second control chamber  35 . This wall portion  47  and the end  46  of the longitudinal groove  44  form control edges, which cooperate with one another to open and block the second coupling path  43 . In this way, a control, whose mode of operation will be described in further detail hereinafter, for the second coupling path  43  is integrated with the injection nozzle  1 . It is clear that preferably a plurality of such longitudinal grooves  44  are provided, in particular distributed over the circumference of the axial portion  41 .  
         [0023]     Alternatively, the second coupling path  43  may for instance also be formed by a line, which is connected directly to the pressure source  37  or directly to the inlet line  36  and hence indirectly to the pressure source  37 . This line could then discharge radially into the first control chamber  28  and could be controlled by the outer jacket of the axial portion  41  as a function of the stroke of the first needle combination  15 .  
         [0024]     Expediently, the first coupling path  39  is disposed or embodied such that is always open, in all the stroke positions of the nozzle needles  7 ,  19 . In this way, when the control valve  32  is closed, filling of the first control chamber  28  and thus a pressure buildup in the first control chamber  28  can be assured in any arbitrary relative position of the nozzle needles  7 ,  19  to one another and relative to the needle body  2 .  
         [0025]     Furthermore, the first coupling path  39  is expediently more severely throttled than the inlet line  36 , so that via the first coupling path  39 , a pressure drop is made possible.  
         [0026]     Expediently, the coupling paths  39  and  43  are adapted to one another such that the first coupling path  39  is more severely throttled than the second coupling path  43 .  
         [0027]     The second coupling path  43  is controllable as a function of the stroke of the first nozzle needle  7 . An axial spacing between the end  46  of the longitudinal groove  44  and the wall portion  47  defines a prestroke  48 , upon which the second coupling path  43  is switched for the sake of opening and closing.  
         [0028]     The inlet line  36  is expediently disposed such that in all the stroke positions that occur of the nozzle needles  7 ,  19 , it is always open and can feed the second control chamber  35 .  
         [0029]     A slaving means  49  is embodied between the first needle combination  15  and the second needle combination  27 . This slaving means  49  is designed such that the first needle combination  15 , upon closure, entrains the second needle combination  27  or at least the second nozzle needle  19  in the closing direction  17 .  
         [0030]     When the nozzle needles  7 ,  19  are open, the injection ports  5 ,  6  are supplied with fuel at high pressure via a fuel supply line  50 . To this end, this fuel supply line  50  is connected to the pressure source or high-pressure fuel line  37 . The fuel supply line  50  discharges into a nozzle chamber  51 , from which an annular chamber  52  leads to the injection ports  5 ,  6 . The first sealing seat  10  is disposed between the at least one first injection port  5  and the annular chamber  52 , so that the first nozzle needle  7  controls the supply of fuel to the at least one first injection port  5 . The second sealing seat  22  is disposed between the at least one second injection port  6  and the annular chamber  52 , so that when the first nozzle needle  7  is open, the second nozzle needle  19  controls the fuel injection through the at least one second injection port  6 .  
         [0031]     The injection nozzle  1  of the invention functions as follows:  
         [0032]     In the outset position shown in  FIG. 1 , the control valve  32  is in the blocking position shown, so that the outlet line  31  is not in communication with the pressure sink  34 . Since the first control chamber  28  moreover communicates, at least via the first coupling path  39  and at short strokes of the first valve combination  15 , indirectly with the pressure source  37  via the second coupling path  43 , the high fuel pressure can build up in the first control chamber  28 . Accordingly, the first control face  29  can introduce a relatively strong closing force into the second needle combination  27  and a resultant force operative in the closing direction  17  is created in the second nozzle needle  19 .  
         [0033]     The second control face  30  introduces a relatively strong closing force into the first needle combination  15 . Moreover, the high fuel pressure also prevails in the second control chamber  35 , so that via the third control face  38  as well, a relatively strong closing force can be introduced into the first needle combination  15 . The restoring force of the restoring spring  16  is operative as well. While the pressure forces on the second control face  30  and the third control face  38  and the restoring forces of the restoring spring  16  act in the closing direction  17 , the high fuel pressure at the pressure step  12  of the first nozzle needle  7  generates a force acting in the opening direction  18 .  
         [0034]     Overall, a resultant force operative in the closing direction  17  can thus build up in the first nozzle needle  7  as well. Consequently, the first nozzle needle  7  is seated in the first seat  10 , and the second nozzle needle  19  is seated in the second seat  22 .  
         [0035]     For opening the first nozzle needle  7 , the control valve  32  is adjusted into the open position, and as a result the outlet line  31  is opened and thus communicates with the pressure sink  34 . Accordingly, a pressure drop occurs in the first control chamber  28 . As a result of this pressure drop, a first pressure value can develop in the first control chamber  28 . Since the outlet line  31  has a throttling action, and since via the coupling paths  39 ,  43 , replenishing hydraulic fluid permanently flows into the first control chamber  28  when line  31  is open, the first pressure value is indeed less than the high fuel pressure, but is at least greater than the pressure of the pressure sink  34 . At the same time, the pressure also drops in the second control chamber  35 . The pressure decrease at the second control face  30  and the third control face  38  leads to reduced closing forces in the first needle combination  15 . The involved components of the injection nozzle  1  are adapted to one another in such a way that in the first nozzle needle  7 , a resultant force operative in the opening direction  18  is established and the first nozzle needle  7  lifts from the first seat  10 .  
         [0036]     As a consequence, an injection of fuel occurs through the at least one first injection port  5 .  
         [0037]     As soon as the first nozzle needle  7  lifts from the first seat  10 , the high fuel pressure is essentially applied to the pressure step  24  of the second nozzle needle  19  as well. The components of the injection nozzle  1  here are adapted to one another in such a way that in the second needle combination  27 , a resultant force acting in the closing direction  17  continues to result, even though the pressure in the first control chamber  28  has been reduced to the first pressure value, and the pressure step  24  of the second nozzle needle  19  is acted upon by the high fuel pressure. For instance, for this purpose, the pressure step  24  of the second nozzle needle  19  is made relatively small. A restoring spring, not shown here, may also be provided, which is braced on the second needle combination  27 , for instance on the first control face  29 , and introduces a corresponding closing force into the second needle combination  27 . Accordingly, even when the first nozzle needle  7  is opening, the second nozzle needle  19  remains in the second seat  22 .  
         [0038]     If the control valve  32  is open long enough, then beginning at the outset position, in which the first nozzle needle  7  is seated in the first seat  10 , the first needle combination  15  executes the predetermined prestroke  48 . As soon as this prestroke  48  has been executed, the control edges, that is the axial end  46  of the longitudinal groove  44  and the wall portion  47  are radially aligned with one another, and as a result the second coupling path  43  is blocked. Because of the blocking or closure of the second coupling path  43 , not as much replenishing hydraulic fluid flows into the first control chamber  28 , so that the pressure there continues to drop, to a second pressure value. In any case, the second pressure value is less than the first pressure value that prevails when the second coupling path  43  is open. Since as before, the first coupling path  39  allows a replenishing flow of hydraulic fluid into the first control chamber  28 , the second pressure value is also higher than the pressure of the pressure sink  34 . The adaptation of the components of the injection nozzle  1  for this state is selected in such a way that the second pressure value at the first control face  29  can now introduce only such slight pressure forces that a resultant force operative in the opening direction  18  is established at the second needle combination  27 , or at the second nozzle needle  19 . Consequently, the second nozzle needle  19  lifts from the second seat  22 . Accordingly, a fuel injection through the at least one second injection port  6  now takes place in addition.  
         [0039]     It is notable here that the first coupling path  39  limits the pressure drop in the first control chamber  28  to the aforementioned second pressure value, so that for the opening stroke of the second nozzle needle  19  or of the second needle combination  27 , only a comparatively low opening speed results. In particular, a hard impact against a stop face, such as an axial wall  53  of the first control chamber  28 , and hence bouncing of the second needle combination  27  can be avoided.  
         [0040]     Furthermore, it is fundamentally possible to design the second needle combination  27  such that it moves in damped fashion against the stop (wall  53 ), which can be achieved for instance by suitable contouring of the first control face  28 .  
         [0041]     As soon as the first nozzle needle  7  has exceeded the prestroke  48 , the kinematics of the first needle combination  15  change as well. For one thing, the reduced pressure force at the second control face  30  has an effect on the balance of forces at the first needle combination  15 . As a result of the blocked second coupling path  43 , the replenishing medium flowing into the second control chamber  35  via the inlet line  36  can now flow out of the second control chamber  35  only via the first coupling path  39 , so that in the second control chamber  35 , a pressure increase occurs. This pressure increase increases the closing force of the third control face  38 , which likewise affects the balance of the forces that engage the first needle combination  15 . Depending on the design, a damping or braking of the first nozzle needle  7  or the first needle combination  15  can be attained.  
         [0042]     If only an injection through the at least one first injection port  5  is wanted, then the control valve  32  must be returned to the blocking position shown in good time, before the first nozzle needle  7  reaches the predetermined prestroke  48 . The axial length of the prestroke  48  can thus be selected as a function of the opening times for the first nozzle needle  7 .  
         [0043]     To close the nozzle needles  7  and  19 , the control valve  32  is shifted to the closing position shown. The result is a sharp pressure increase in both the first control chamber  28  and the second control chamber  35 , with the consequence that the balance of forces at the first needle combination  15  is reversed again, resulting in a force in the closing direction  17  that drives the first needle combination  15  ahead in the closing direction  17 . Since with the second nozzle needle  19  open, the high fuel pressure engages the second seat cross section in the opening direction  18  as well, it can happen that the balance of forces at the second needle combination  27 , despite the high pressure at the first control face  29 , does not produce closing force, or only a relatively slight resultant closing force. In this case, the slaving means  49  assures that the first needle combination  15  carries the second needle combination  27 , or at least the second nozzle needle  19 , along with it. As soon as the first nozzle needle  7  arrives in the first seat  10 , the pressure downstream of the first seat  10  drops abruptly, so that then the second needle combination  27 , or the second nozzle needle  19 , moves into the second seat  22  as well.  
         [0044]     The foregoing relates to a preferred exemplary embodiment 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.