Patent Publication Number: US-2016230728-A1

Title: Plunger And Fluid-Line System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage application of International Application No. PCT/EP2014/070829 filed Sep. 29, 2014, which designates the United States of America, and claims priority to DE Application No. 10 2013 220 547.3 filed Oct. 11, 2013, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure generally relates to control-plunger/control-bore arrangements and, more specifically, to a control piston-control bore arrangement for an injector which may be used as a fuel injector for a direct injection system of a motor vehicle. 
     BACKGROUND 
     Ever more stringent legal regulations with regard to admissible pollutant emissions of internal combustion engines for motor vehicles necessitate the use of fuel injectors to achieve improved mixture preparation in the cylinders of the internal combustion engines. In the case of such injectors, control of an injection of fuel is performed by way of a nozzle needle which is mounted displaceably in the injector and which, in a manner dependent on the stroke thereof, opens up and closes off again an opening cross section or one spray hole or a multiplicity of spray holes of a nozzle assembly of the injector. An actuation of the nozzle needle is performed for example by way of a piezoelectric actuator, which actuates the nozzle needle hydraulically or mechanically. 
     To reduce the pollutant emissions of the internal combustion engine and at the same time keep the fuel consumption thereof as low as possible, it is desirable to achieve optimized combustion within the cylinders of the internal combustion engine. For good process implementation and/or control/regulation of a combustion in the cylinders, it is necessary for the fuel to be injected to be able to be dosed in as exact a manner as possible in terms of volume and time in order, at all times, to achieve optimized combustion and/or the most complete possible regeneration of a particle filter of the motor vehicle, because torque demands of the internal combustion engine are converted into injection quantities, which in turn correlate with an injection duration in a manner dependent on an injection pressure, a stroke of the nozzle needle and a geometry of the injector. 
     A deviation of an actual injection quantity—a so-called shot—from a setpoint injection quantity of the injector always has an adverse effect on a combustion, that is to say on the pollutant emissions generated thereby, and normally also on fuel consumption of the internal combustion engine. For directly injecting injectors, high demands exist with regard to accuracy of the injection quantities and a stability of a jet pattern under all operating conditions and over an entire service life of the injector. This applies in particular with regard to small injection quantities in a multiple-injection mode with the associated short injection intervals, and/or in a partial lift mode of a nozzle needle. 
     In a modern injector, to ensure the least possible shot-to-shot variance, it is necessary for a fluid pressure in a control chamber of the injector to be maintained as exactly as possible, in a manner dependent on a rail pressure, during an injection interval. Said pressure is set in a manner dependent on flow resistances in the individual leakage paths (inflowing and outflowing) of the injector. Since a flow resistance of a control piston (piston) of the injector, which is paired with a control bore (fluid line) with a defined fit, is dependent on a positioning of the piston (centrally, eccentrically, tilted) in the control bore, this yields an influence on a control chamber pressure that is set, and thus on an injection quantity. Stochastic fluctuations of said pressure owing to fluctuating positioning of the control piston in the control bore lead to increased stochastic fluctuations of the injection quantities, that is to say to increased shot-to-shot variance. 
     SUMMARY 
     The present disclosure relates to systems for a fluid pressure in a fluid chamber to be reproducibly set by way of a piston in a fluid line, wherein it should be possible for a position of the piston in the fluid line to be set in a reproducible manner. In particular, a fluid pressure in a control chamber of an injector, in particular of a fuel injector, may be set or maintained as exactly as possible, in a manner dependent on a rail pressure, during an injection interval. It is thereby intended to improve, for example, shot-to-shot variance, in particular for a hydraulically directly driven injector. 
     In some embodiments of the present teaching, the piston-fluid line arrangement comprises a piston, which is fitted in or paired with a fluid line and which can be positioned sideward hydraulically by way of a fluid passing through the fluid line, wherein a geometry of the piston and/or a geometry of the fluid line are/is configured such that the piston can be positioned, and/or is positioned, eccentrically in the fluid line by the fluid. The geometry of the piston may be a secondary geometry, wherein a primary geometry of the piston may be cylindrical. Likewise, the geometry of the fluid line may be a secondary geometry, wherein a primary geometry of the fluid line likewise may be cylindrical. The injector may have a piston-fluid line arrangement, in particular a control piston-control bore arrangement. 
     In some embodiments, the secondary geometry of the piston and/or the secondary geometry of the fluid line are/is configured such that a centerline of the piston can be positioned, and/or is positioned, substantially parallel to a centerline of the fluid line by the fluid. Furthermore, the geometry/geometries may be selected such that a throughflow of the fluid between the piston and the fluid line (sealing gap) is greater than a throughflow in the case of a concentric position of the piston in the fluid line. In this case, it is possible for the throughflow of the fluid between the piston and the fluid line to be set as a substantially maximum throughflow. Here, the piston assumes a substantially intensely eccentric position in relation to the fluid line. Such an embodiment may be advantageous in some applications, wherein a greatest minimum throughflow is set in the case of a given fit or pairing of the piston and the fluid line. 
     In some embodiments, the secondary geometry of the piston and/or the secondary geometry of the fluid line are/is configured such that an asymmetrical pressure distribution of the fluid can be set, and/or is set, in a sealing gap between a shell face of the piston and an internal face of the fluid line. Furthermore, the geometry/geometries may be selected such that, in the shell face of the piston and/or the internal face of the fluid line, there is provided a fluid path by way of which the asymmetrical pressure distribution of the fluid in the sealing gap can be set and/or is set. 
     Furthermore, the geometry/geometries may be selected such that, in the shell face of the piston and/or the internal face of the fluid line, the fluid path is provided such that a sideward force can be exerted, and/or is exerted, on the piston by way of the fluid. The asymmetrical pressure distribution of the fluid in the sealing gap gives rise to the sideward force of the fluid on the piston, wherein the sideward force is intended to act on the piston, that is to say the asymmetrical pressure distribution on the piston is intended to be set, such that the centerline of the piston is oriented parallel to, and shifted in a parallel manner with respect to, the centerline of the fluid line. 
     In some embodiments, the fluid path may be formed such that the piston is permanently securely positioned in an eccentric position during relevant operating states and, in this case, the throughflow of the fluid through the sealing gap is relatively low. In the case of a given pressure difference at the piston, a target throughflow of fluid through the sealing gap may be primarily as constant as possible and secondarily as small as possible. A relatively large eccentricity of the piston also entails a relatively large throughflow of fluid through the sealing gap, and it is therefore preferable to seek a reliable eccentric position in which the throughflow of the fluid through the sealing gap that is generated is relatively low. That is to say, a relatively slight eccentric position, which is however geometrically constant over time, of the piston in the fluid line. 
     In some embodiments, the fluid path may be provided on/in the piston and/or on/in the fluid line. The explanations below relate primarily to the piston and are also transferable, where it appears to be expedient, to the fluid line. It is accordingly possible for the fluid path on/in the piston to be configured such that it can be placed in fluidic communication with a high-pressure side or with a low-pressure side of the piston. Here, the fluid in the fluid path forces the piston away from an opening of the fluid path on/in the piston, and/or the fluid in the sealing gap forces the piston toward an opening of the fluid path on/in the piston. The low-pressure side is to be understood to mean a face region of the piston, in which a fluid pressure prevails which is lower than that at the high-pressure side of the piston. Said pressure difference may be even only a few bar, wherein it is by all means possible for a fluid high pressure to prevail on the low-pressure side. 
     That is to say, for the former case, the fluidic connection of the fluid path to the high-pressure side of the piston, the fluid in the fluid path forces the piston away from the opening of the fluid path in the direction of a region, situated radially opposite said fluid path, of the internal face of the fluid line. Also, for the second case, that is to say the fluidic connection of the fluid path to the low-pressure side of the piston, the fluid in the sealing gap forces the piston in the direction of the opening of the fluid path at a region, situated directly opposite the opening, of the internal face of the fluid line. 
     In some embodiments, the fluid path may have a recess on/in the piston, wherein the recess is in particular a groove or facet which runs, in sections, in a circumferential direction and/or, in sections, in a longitudinal direction of the piston. A base of the recess may be planar or curved, that is to say the base of the recess has, for example, a radius. Such embodiments are relatively easily transferable to the fluid line. Furthermore, the fluid path may have a fluidic connection of an interior and an exterior of the piston, wherein the fluidic connection is in particular a bore, preferably a passage bore and/or an intersection, preferably of an internal and external recess of the piston. 
     In some embodiments, the fluid path on the outside of the piston may have the opening, a circumferential groove, a circumferential facet, a longitudinal groove and/or a longitudinal facet. Furthermore, the fluid path may comprise at least one bore from an outer side of the piston to a piston interior. Furthermore, the fluid path may have an intersection of an external recess with an internal recess and/or a cutaway portion on a longitudinal end section of the piston. According to the invention, the piston may be in the form of a control piston, a pin, a control pin or a leakage pin. In the case of a fuel being used, the fluid is preferably a diesel or gasoline fuel. 
     In some embodiments, it is possible for a fluid pressure in a fluid chamber to be set by way of a reproducible piston position in a fluid line. Here, a position of the piston in the fluid line is set by way of a geometry of the piston and/or of the fluid line. Here, the invention is particularly suitable for use on injectors, in particular fuel injectors, wherein, during an injection interval, a fluid pressure in a control chamber of the injector can be set or maintained in an effective manner. That is to say, the shot-to-shot variance of the injector is improved. Furthermore, a variance with regard to an injector function in a mass production context is reduced, and a fraction of injectors which do not conform to demanded tolerances in terms of their injection quantities can be reduced. It is thus also possible for outlay with regard to required reworking to be reduced. This results, individually and overall, in a reduction in production costs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be discussed in more detail below on the basis of exemplary embodiments with reference to the appended drawing. Elements or components which have an identical, univocal or analogous form and/or function are denoted by the same reference designations in different figures of the drawing. 
       In the schematic figures of the drawing, 
         FIG. 1  shows a longitudinal side view of an injector according to the invention for a common-rail injection system of an internal combustion engine, said injector being illustrated in centrally sectioned form in the middle and at the bottom; 
         FIG. 2  shows a centrally sectioned, detailed longitudinal side view, cut away at the top and bottom, of a control assembly of the injector from  FIG. 1 , with a hydraulic direct drive of a nozzle needle; and 
         FIGS. 3 to 5  show a first embodiment, 
         FIGS. 6 to 8  show a second embodiment, 
         FIGS. 9 to 11  show a third embodiment, 
         FIGS. 12 to 14  show a fourth embodiment, 
         FIGS. 15 to 17  show a fifth embodiment, 
         FIGS. 18 to 20  show a sixth embodiment, and 
         FIGS. 21 to 23  show a seventh embodiment, of a piston-fluid line arrangement according to the teachings of the present disclosure, in particular of a control piston-control bore arrangement. 
     
    
    
     Here, a respectively first figure of the embodiments is a sectional side view, and a respectively second figure is a sectional plan view of a control plate of the injector. The respectively third figure of the embodiments is in this case a perspective view of a control piston of the injector. Furthermore,  FIGS. 24 and 25  show two embodiments of the use of the invention on a fluid line. 
     DETAILED DESCRIPTION 
     The invention will hereinafter be discussed in more detail on the basis of a piezoelectrically operated common-rail diesel injector  1  for an internal combustion engine (see  FIG. 1 ). The teachings of the present disclosure are not limited to use with such diesel injectors  1 , but may for example also be applied to pump-nozzle injectors or gasoline injectors with a unipartite or multi-part nozzle needle. For gasoline injectors, typical designations can be found in the list of reference numerals. An injectable fluid may be a fuel, though it is self-evidently possible for an injector  1  according to the invention to be used for the injection of some other fluid, such as for example water, an oil or any other desired process fluid; that is to say, the injector  1  is not restricted to the automobile industry. 
       FIG. 1  shows the injector  1  substantially in a sectional view, wherein the injector  1  comprises a nozzle assembly  10  and an injector assembly  50 . The nozzle assembly  10  and the injector assembly  50  are fixed to one another in fluid-tight fashion by way of a nozzle clamping nut  60 . The injector assembly  50  has an injector body  500  in which an actuator  510 , which is preferably in the form of a piezo actuator  510 , is provided. Use may however also be made of an electromagnetic actuator. In the present example, the piezo actuator  510  hydraulically directly drives a unipartite, preferably integral, nozzle needle  110  (see also  FIG. 2 ). The nozzle needle  110  may also be of two-part or multi-part form, and/or be designed to open outwardly in the injector  1 . 
     The injector body  500  has a high-pressure-side fluid port (not illustrated) for the fuel to be injected, wherein the fluid port is in fluidic communication with a high-pressure bore  502  formed in the injector body  500 . By way of the high-pressure-side fluid port, the injector  1  can be hydraulically connected to a high-pressure fluid circuit (not illustrated). The high-pressure bore  502  supplies fuel at high pressure, for example a so-called rail pressure (common-rail system), to the nozzle assembly  10  and thus to a nozzle chamber  102  of the injector  1 . During the operation of the injector  1 , an actually high or maximum pressure substantially always prevails in the nozzle chamber  102 . 
     The nozzle assembly  10  has a nozzle body  100  with at least one spray hole (not illustrated) in its nozzle  104  and the nozzle chamber  102 , wherein the nozzle needle  110  is arranged displaceably, and mounted in sections, in the nozzle chamber  102 . The nozzle needle  110  is forced in the direction of its nozzle needle seat at the inside in the nozzle  104  by way of an energy store  114 , preferably a nozzle needle spring  114 , so as to be reliably closed even in an electrically deenergized state of the piezo actuator  510 . In a manner dependent on an actuation of the piezo actuator  510 , the nozzle needle  110  is either forced into its nozzle needle seat or moved away from the nozzle needle seat, whereby fuel can be injected. 
     The nozzle assembly  10  furthermore accommodates a control assembly  20 , which is situated between the nozzle body  100  and the injector assembly  50 , for the control of the nozzle needle  110  on the basis of a lengthening of the piezo actuator  510  in a manner dependent on the energy or charge of said piezo actuator, that is to say in a manner dependent on an electrical voltage applied to said piezo actuator.  FIG. 2  shows the components of the control assembly  20  for a direct hydraulic coupling by way of a lengthening movement of the piezo actuator  510  and a resulting movement of the nozzle needle  110 . The piezo actuator  510  has, for this purpose, a base plate  512  with a preferably integral actuating projection which is in direct mechanical contact with a transmission pin  214  which is, with a very small clearance, fitted in and/or paired with a pin bore  212  of an intermediate plate  210  of the control assembly  20 . 
     A pairing clearance of the transmission pin  214  in the pin bore  212  is selected to be so small, for example approximately 1 μm, that, even in the presence of a high rail pressure of up to over 2500 bar, only a small amount of fuel leakage occurs at the transmission pin  214 . Here, the pin bore  212  connects a first control chamber  22 , which is also referred to as piston control chamber  22  and in which a fuel pressure prevails which is slightly lower than the actual rail pressure, to a leakage chamber  52  of the injector  1 , which leakage chamber is preferably in permanent fluidic communication with an ambient pressure. The leakage chamber  52  is preferably in fluidic communication with a leakage port  504  of the injector  1 . A relatively very high pressure difference prevails at the transmission pin  212 , which pressure difference may by all means exceed a value of 2450 bar, for example in the case of an assumed maximum pressure of 2500 bar and when the injector  1  is closed. 
     The first control chamber  22  is preferably in permanent fluidic communication, by way of a connecting bore  14  in a section of the control assembly  20 , with a second control chamber  12 , the so-called needle control chamber  12 . As in the first control chamber  22 , a fuel pressure slightly lower than the rail pressure prevails in the second control chamber  12 , wherein the pressures in the control chambers  12 ,  22  are substantially equal at least when the injector  1  is closed. A fluid throttle (not illustrated), which is preferably formed in a separate plate  230  of the control assembly  20 , may be provided in the connecting bore  14 . 
     A stroke (lengthening) of the piezo actuator  510  is transmitted by way of the transmission pin  214 , which is also referred to as leakage pin  214 , to a control piston  300  which is fitted in and/or paired with a control bore  400  of a control plate  220  of the control assembly  20 . The transmission pin  212  engages, at/in the first control chamber  22 , on an upper face surface of the control piston  300 , wherein the control piston  300  is supported, on an internal face surface, by an energy store  224 , which is preferably in the form of a spiral spring  224 . It is preferable for substantially rail pressure to prevail at the internal face surface and at an underside of the control piston  300 , wherein said region is preferably in permanent fluidic communication, through a connecting bore  232 , with the nozzle chamber  102 . 
     In the present examples, the control piston  300  is in the form of a sleeve  300  which is closed at the top side (side of the first control chamber  22 ) and into the interior  340  of which the spring element  224  for the restoring movement of the control piston  300  projects. It is self-evidently possible for the control piston  300  to be in the form of a solid cylinder, wherein then, the spring element  224  engages on a bottom side of the control piston  300 , and the spring element  224  may be mounted for example in a bore in the plate  230 . Mixed forms between the illustrated sleeve-shaped control piston  300  and a control piston  300  in the form of a solid cylinder are also self-evidently possible. 
     The second control chamber  12  is formed by a face surface of an upper longitudinal end section  112  of the nozzle needle  110 , the so-called needle piston  112 , by a wall of a needle bore  122  in an upper guide  120  of the nozzle needle  110 , preferably in a nozzle needle sleeve  120 , and by a lower face surface of the plate  230 . The needle piston  112  of the nozzle needle  110  is in this case averted from a nozzle needle tip of the nozzle needle  110  or of the nozzle  104  of the nozzle body  100 . This embodiment of the injector  1 , presented here briefly, is not to be regarded as being restrictive. The invention is self-evidently applicable to a multiplicity of other embodiments of injectors. 
     As a result of a movement of the control piston  300  owing to a stroke of the piezo actuator  510  (via the transmission pin  214 ), a pressure drop is generated in the first control chamber  22 , which pressure drop is transmitted via the connecting bore  14  and, possibly with a time delay, through the optional fluid throttle in the plate  230 , to the upper face surface of the nozzle needle  110  in the second control chamber  12 . If said pressure drop exceeds a particular value, the nozzle needle  110  opens, and an injection of fuel (shot) takes place. A stroke of the nozzle needle  110  can, proceeding from an opening of the nozzle needle  110 , be controlled or regulated by way of a variation of the stroke of the piezo actuator  510 . The stroke of the piezo actuator  510  may in this case be changed by way of a variation of the intrinsic electrical energy thereof. 
     During the discharging of the piezo actuator  510 , the length of the latter decreases. By way of the rail pressure, acting on the internal face surface (bottom side) of the control piston  300 , from the nozzle chamber  102  together with the force, likewise acting in said direction, of the spring element  224 , the control piston  300  is pushed back into its initial position, which is determined by a position of the transmission pin  214 . In this way, the nozzle needle  110  is, corresponding to the movement of the piezo actuator  510 , moved into its closed position again, and an injection of fuel is ended. The nozzle needle spring  114  then holds the nozzle needle  110  securely closed on its seat in the nozzle  104  of the nozzle body  100 . 
     It is an aim of the invention to ensure the least possible shot-to-shot variance of the injections. Here, it is necessary for the fluid pressure in the control chamber  12 ,  22  to be set as exactly as possible and reproducibly, in a manner dependent on the rail pressure, during an injection interval. This reproducible behavior may then be taken into consideration in the actuation of the piezo actuator  510 . A fluid pressure that is set in the control chamber  12 ,  22  is influenced to a great extent by the control piston  300  (generally also: piston  300 ) and the control bore  400  (generally also: fluid line  400 ). Here, in addition to a fixed, tolerance-afflicted size of a sealing gap  222  between the control piston  300  and the control bore  400 , a position of the control piston  300  in the control bore  400  is also of significance, because fluctuating positions of the control piston  300  in the control bore  400  lead to increased shot-to-shot variance. 
     Possible positions of the control piston  300  in the control bore  400  are substantially a concentric position, an eccentric position and a tilted position. By way of these different positions of the control piston  300 , the flow resistances in the control bore  400  vary significantly owing to a gap geometry resulting from the respective position. The flow of fluid through the sealing gap  222  in the case of a maximally eccentric position of the control piston  300  is increased by a factor of approximately 2.5 in relation to the concentric position of said control piston. In the case of a maximally tilted position of the control piston  300 , said factor is only approximately 0.5. That is to say, five times as much fluid can flow through the sealing gap  222  per unit of time in the case of a maximally eccentric position of the control piston  300  than in the case of a maximally tilted position (in an injector  1 ). This has significant effects on the pressures, set during the injection intervals, in the control chambers  12 ,  22 , in particular in the first control chamber  22 . 
     The solution according to the invention to this problem consists in the use of a geometry of the control piston  300  (cf.  FIGS. 3 to 23 ) and/or a geometry of the control bore  400  (cf.  FIGS. 24 and 25 ) to influence a position of the control piston  300  in the control bore  400 . This is preferably performed in such a way that primarily a reliable eccentric and non-concentric and non-tilted position of the control piston  300  in the control bore  400  is sought. It is secondarily the case that, in said reliable eccentric position, a throughflow of the fluid (in this case fuel) through a sealing gap  222  that is set should be relatively small. The corresponding geometry or the corresponding geometries are in this case selected such that a centerline  302  of the control piston  300  is oriented parallel to a centerline  402  of the control bore  400 , wherein the two centerlines  302 ,  402  are not aligned with one another but rather are spaced apart from one another, in particular are not maximally spaced apart from one another. 
     In some embodiments, the control piston  300  is modified at its shell face  304 , and/or the control bore  400  is modified at its internal face  404 , such that a resultant sideward force on the control piston  300  is generated, which ensures an eccentric preferential position of the control piston  300  in the control bore  400 . This yields stochastic fluctuations of the injection quantities at a relatively low level even in the presence of high rail pressures. Such a modification is realized preferably by way of a fluid path  310 ,  410  on/in the control piston  300  and/or on/in the control bore  400 , which fluid path opens at the control piston  300  (opening  312 ,  412 ). 
     Here, the fluid path  310 ,  410  may be a groove, for example a circumferential groove and/or a longitudinal groove, a facet, for example a circumferential facet and/or a longitudinal facet, a cutaway portion and/or a fluidic connection such as a bore, a passage bore and/or an intersection etc. or any desired combination of these. According to this specification, all of these expressions are intended to be subsumed under the expression “recess”, in the sense of deviations from a primary geometry of the control piston  300  and/or of the control bore  400 . The primary geometry of the control bore  400  or of the control piston  300  is the shape of a (hollow) cylinder or of a (hollow) cone. The control piston  300  may in this case be a part or a section of another component, for example a needle piston  112  of a nozzle needle  110 , a valve body or a part or section thereof etc. This applies analogously to the control bore  400 , which need not imperatively be formed in the control plate  220 . 
     An opening  312 ,  412  of the fluid path  310 ,  410 , constructed from one recess or a multiplicity of recesses  320 ,  322 ;  422 ,  426 , is in this case designed such that the centerlines  302 ,  402  of the control piston  300  and of the control bore  400  are spaced apart from and substantially parallel to one another. Here, it is particularly preferable for the sideward force exerted on the control piston  300  by the fluid passing through the opening  312 ,  412  (said sideward force resulting from the asymmetrical pressure distribution owing to the opening  312 ,  412 ) to engage on the control piston  300  substantially longitudinally in the center, such that substantially no tilting moment is exerted on the control piston  300 . This may have the result that the opening  312 ,  412  itself is provided eccentrically on the control piston  300  (cf.  FIG. 5 ), because the pressure conditions in the sealing gap  222  change from the high-pressure side to the low-pressure side, wherein the sealing gap  222  acts as a fluid throttle. According to the invention, the fluid path  310 ,  410  of the control piston  300  and/or of the control bore  400  may be in communication with the high-pressure side ( FIGS. 3 to 24 ) or with the low-pressure side ( FIG. 25 ). The fluidic communication of the fluid path  310 ,  410  with the low-pressure side is a hydraulic reversal of the fluidic communication of the fluid path  310 ,  410  with the high-pressure side. In the former case, a positive pressure at the opening  312 ,  412  on the control piston  300  serves to realize a parallel offset of the control piston  300  in relation to the control bore  400 . In the second case, a negative pressure at the opening  312 ,  412  on the control piston  300  serves to realize a parallel offset of the control piston  300  in relation to the control bore  400 . 
     Below, a general embodiment of the invention will firstly be discussed in more detail with reference to  FIGS. 3 to 23 . Subsequently, the—self-evidently not exhaustive—seven embodiments of the invention, pertaining to the control piston  300  or a piston  300 , will be briefly discussed. These explanations are however analogously transferable to the control bore  400  or to a fluid line  400 , depending on whether this appears expedient. In this regard, see  FIGS. 24 and 25 , which show two embodiments of the invention in which the concept according to the invention is applied to the control bore  400  or to the fluid line  400 . In particular,  FIG. 25  shows a fluid path  410  fluidically connected to the low-pressure side (first control chamber  22 ). This is intended to illustrate that any fluid paths  310  of the control piston  300  may also be hydraulically connected to the low-pressure side (cf. above). 
     A major design feature is that one recess or a multiplicity of recesses  320 —fluid path  310  or a section thereof—in possibly different geometries are formed on/in the shell face  304  of the control piston  300  on one side. Said recesses  320  lead to the asymmetrical pressure distribution in the sealing gap  222 , giving rise to the resultant sideward force which moves the control piston  300  into its eccentric preferential position. Since a piston interior  340  or a bottom side of the control piston  300  is acted on substantially with the rail pressure of the injector  1 , a pressure substantially at the level of the rail pressure prevails in the fluid path  310 . 
     On a side of the sealing gap  222  situated opposite the opening  312  of the fluid path  310  on the central piston  300 , the fluid pressure falls, over an entire length of the sealing gap  222 , from the rail pressure to the fluid pressure of the first control chamber  22 . The varying pressure profile along the sealing gap  222  in the longitudinal direction of the control piston  300 , between a side of the opening  312  of the fluid path  310  and a side averted therefrom, yields the abovementioned resultant sideward force on the control piston  300 . 
     A width (circumferential direction of the control piston  300 ) and height (longitudinal direction of the control piston  300 ) and an axial position of the opening  312  determine the hydraulic sideward force on the control piston  300 . An advantageous and possibly “optimum” design for the injector  1  provides a hydraulic sideward force which permanently reliably positions the control piston  300  eccentrically (the sideward force is in this case greater than a sum of possible “disturbance” forces, such as for example a transverse force arising from the spring element  224 ), wherein the hydraulic sideward force on the control piston  300  in this case is, or remains, preferably relatively small, in particular minimal. 
     In the example embodiment of the invention as illustrated in  FIGS. 3 to 5 , as a recess  320 , a groove  324  running in a circumferential and longitudinal direction of the control piston  300  is formed into the shell face  304  of the control piston  300  (external recess  320 ). The circumferential groove  324  is in fluidic communication, by way of a fluidic connection  330 , in particular a passage bore  332 , with the piston interior  340 , which connects a base of the circumferential groove  324  to the piston interior  340  in a preferably radial direction. The base of the circumferential groove  324  may, as can be seen in  FIG. 4 , have a radius which is for example greater than that of the control piston  300 . The base may self-evidently also be planar (cf.  FIG. 13 ). A delimitation of the circumferential groove  324  at the shell face  304  forms the opening  312  of the fluid path  310 . In the second embodiment of the invention, as illustrated in  FIGS. 6 to 8 , it is the case that, instead of the circumferential groove  324  in the first embodiment, two fluidic connections  330 , in particular two passage bores  332 , are formed in a wall of the control piston  300 , preferably so as to run in a radial direction. Here, the passage bores  332  are situated on one side of the control piston  300 , and an angle of the centerlines thereof is preferably less than 120°, in particular less than 90° and particularly preferably less than 45°. The delimitations of the passage bores  332  at the shell face  304  together form the opening  312  of the fluid path  310 . It is self-evidently possible for only one passage bore or a multiplicity of passage bores to be provided through the wall of the control piston  300 . 
     In the third embodiment of the invention as illustrated in  FIGS. 9 to 11 , the fluid path  310  comprises an external recess  320  which is in the form of a longitudinal facet  326  or longitudinal groove  326 . Here, a surface  326  is ground or formed on the control piston  300  over a certain length and width (circumferential direction of the control piston  300 ), which surface is open toward the side of the rail pressure, or else for example toward the side of the first control chamber  22  (not illustrated, cf.  FIG. 25 ). A base of the longitudinal facet  326  or longitudinal groove  326  may, as can be seen in  FIG. 10 , be planar, though a radius analogous to  FIG. 4  may also be used. A delimitation of the longitudinal groove  326  or longitudinal facet  326  at the shell face  304  forms the opening  312  of the fluid path  310 . 
     In the fourth embodiment of the invention illustrated in  FIGS. 12 to 14 , and in the fifth embodiment of the invention illustrated in  FIGS. 15 to 17 , the fluid path  310  comprises, in each case proceeding from the rail-pressure side of the control piston  300 , a narrow external recess  320  which is formed as a longitudinal connecting groove  326  in the shell face  304  of the control piston  300 . In the direction of the side of the first control chamber  22 , the respective longitudinal connecting groove  326  opens into an external recess  320  which is formed in each case as a circumferential groove  324 . A delimitation of the circumferential groove  324  and, to a small extent, a delimitation of the longitudinal connecting groove  326  at the shell face  304  together form the opening  312  of the fluid path  310 . 
     The fourth embodiment is characterized in that a base of the circumferential groove  324  is planar ( FIG. 13 ), whereas, in the case of the fifth embodiment, a base of the circumferential groove  324  has a radius ( FIG. 16 ), which in turn may be greater than that of the control piston  300 . Furthermore, the circumferential groove  324  of the fifth embodiment covers a larger region on the outside of the control piston  300  than the circumferential groove  324  of the fourth embodiment. In the first case, the circumferential groove  324  covers approximately 90°, and in the second case, the circumferential groove covers approximately 30-45°. Furthermore, the longitudinal connecting groove  326  may be formed into the wall of the control piston  300  with a smaller depth, equal depth or greater depth than the circumferential groove  324  in the region adjoining the latter. 
     In the sixth embodiment of the invention as illustrated in  FIGS. 18 to 20 , the fluid path  310  comprises an external recess  320  which is in the form of a circumferential groove  324 . A base of the circumferential groove  324  has, in turn, a radius (see above), though may also be of planar form. The base of the circumferential groove  324  is fluidically connected to the piston interior  340  via an intersection  334  formed as a fluidic connection  330 . The intersection  334  is produced by way of a longitudinal groove  322 , in the form of an internal recess  322 , in the piston interior  340 . That is to say, the fluidic connection  330  of the circumferential groove  324  to the side of the rail pressure is produced by way of the intersection  324  with the longitudinal groove  322  in the longitudinal direction of the control piston  300  on an inner side of the control piston  300 . A delimitation of the circumferential groove  324  on the shell face  304  forms the opening  312  of the fluid path  310 . 
     In the seventh embodiment of the invention as illustrated in  FIGS. 21 to 23 , the fluid path  310  comprises a recess  328  or a cutaway portion  328  of a wall of the control piston  300 , that is to say a piston skirt of the control piston  300  is shortened on one side over a certain circular segment. A delimitation of the cutaway portion  328  at the shell face  304  in this case forms the opening  312  of the fluid path  310 . 
     These exemplary embodiments of the invention may self-evidently also be applied to control pistons  300  which are not of hollow-bored form. In such a situation, it may be necessary for a preferably small bore to be formed into the control piston  300 . Furthermore, said features may also be applied to other fit and/or pairing clearances in the injector  1 , for example to the transmission pin  214  in the pin bore  212 , to the nozzle needle  110  in the nozzle needle sleeve  120 , etc., which in particular influence a leakage balance (inflowing equal to outflowing) and thus also a resultant pressure in the control chamber  12 ,  22 . Furthermore, the invention is generally applicable to hydraulic coupling elements  300 , that is to say the control piston  300  is in the form of a hydraulic coupling element  300 . 
     Below, two exemplary embodiments of the invention will be briefly discussed, wherein the respective recess  422  is provided not on/in the control piston  300  but on/in the internal face  404  of the control bore  400  (fluid line  400 ). 
     In the eighth embodiment of the invention as illustrated in  FIG. 24 , the fluid path  410  of the control bore  400  comprises an internal recess  422  which is in the form of a longitudinal facet  426  or longitudinal groove  426 . Here, a surface  426  or recess  426  is ground or formed into the internal face  404  of the control bore  400  over a certain length and width (circumferential direction of the control bore  400 ), which surface or recess is open toward the side of the rail pressure. Said surface or recess may however also be open toward the side of the first control chamber  22  (not illustrated, cf.  FIG. 25 ). A base of the longitudinal facet  426  or longitudinal groove  426  may, as can be seen in  FIG. 10 , be planar, though a radius analogous to  FIG. 4  may also be used, wherein the radius is preferably smaller than that of the control bore  400 . A delimitation of the longitudinal facet  426  or longitudinal groove  426  at the internal face  404  forms the opening  412  of the fluid path  410  of the control bore  400  on the control piston  300 . 
     In the ninth embodiment of the invention as illustrated in  FIG. 25 , the fluid path  410  of the control bore  400  comprises an internal recess  422  which is in the form of a narrow longitudinal groove  426  and which is open toward the side of the first control chamber  22 . A delimitation of the longitudinal groove  426  at the internal face  404  substantially forms the opening  412  of the fluid path  410  of the control bore  400  on the control piston  300 . During operation of the injector  1 , substantially a fluid pressure of the low-pressure side or of the first control chamber  22  prevails in the longitudinal groove  426 . Here, the internal recess  422  is such, in particular is formed so as to run in the longitudinal direction of the control bore  400  in such a way, that an asymmetrical pressure distribution of the fluid on the control piston  300  is realized, wherein the control piston  300  is pulled by suction in the direction of the opening  412  of the fluid path  410 , or is pushed from a side situated opposite this by the fluid pressure in the sealing gap  222 . 
     Such hydraulically reversed embodiments of the invention are generally applicable. Here, the pressure conditions at the control piston  300  in a radial direction of the control piston  300  are at least qualitatively reversed. That is to say, a pressure side and a suction side at the control piston  300  change their positions. For embodiments one to seven of the invention, this means that the fluid path  310  of the control piston  300  is open toward the low-pressure side, and opens out in the sealing gap  222  on the control piston. A fluidic connection to the piston interior  340  must in this case self-evidently be prevented. 
     A simple embodiment of the invention which is not illustrated is a pressure duct through a control piston  300  in the form of a solid cylinder. Here, it is for example the case that two intersecting blind bores are formed in the control piston  300 . One bore extends axially from the low-pressure side into the control piston  300 , and the other extends radially to said first bore and intersects the latter within the control piston  300 . Then, in the injector  1 , a pressure duct exists from the low-pressure side on one side into/to the sealing gap  222  between the control piston  300  and the control bore  400 . Said embodiment may self-evidently be hydraulically reversed, wherein the first blind bore is formed in the control piston  300  so as to extend not from the low-pressure side but from the high-pressure side. In the case of a fully rotationally symmetrical control piston  300 , this may be simply reversed in order to move from this embodiment to the other embodiment. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Injector, fuel injector, common-rail/piezo fuel injector, pump-nozzle fuel injector, diesel injector, gasoline injector 
           10  Nozzle assembly, injection module 
           12  Second control chamber, needle control chamber 
           14  Connecting bore/line between first  22  and second control chamber  12   
           20  Control assembly of the nozzle assembly  10  for the control of the nozzle needle  110   
           22  First control chamber, piston control chamber 
           50  Injector assembly, drive module 
           52  Leakage chamber 
           60  Nozzle clamping nut, valve clamping nut 
           100  Nozzle body 
           102  Nozzle chamber, nozzle bore 
           104  Nozzle, injection nozzle, valve 
           110  Nozzle needle, injection needle, possibly in two or multiple parts, inwardly or outwardly opening 
           112  Upper longitudinal end section of the nozzle needle  110 , needle piston, averted from the nozzle  104  and/or from a valve of the injector  1   
           114  Energy store, spring element, spiral spring, compression spring, nozzle needle spring, injection needle spring, for mechanical preloading of the nozzle needle  110   
           120  (upper) guide of the nozzle needle  110 , nozzle needle sleeve 
           122  Needle bore 
           210  Intermediate plate 
           212  Pin bore 
           214  Transmission pin, leakage pin 
           220  Control plate 
           222  Sealing gap between piston  300  and fluid line  400   
           224  Energy store, spring element, spiral spring, compression spring, for preloading of the piston  300   
           230  Plate 
           232  Connecting bore 
           300  Piston, control piston, hydraulic coupling element 
           302  Centerline of the piston  300304  Shell face, shell surface, shell side of the piston  300   
           310  Fluid path on/in the piston  300   
           312  Opening of the fluid path  310  on the piston  300   
           320  (External) recess, external recess 
           322  (Internal) recess, internal recess 
           324  Groove, facet, circumferential groove, circumferential facet, recess 
           326  Groove, facet, longitudinal groove, longitudinal facet, recess 
           328  Cutaway portion, recess 
           330  Fluidic connection between the interior and exterior of the piston  300 , recess 
           332  Bore, passage bore, fluidic connection, recess 
           334  Intersection, fluidic connection, recess 
           340  Piston interior, interior 
           400  Fluid line, control bore, piston bore 
           402  Centerline of the fluid line  400   
           404  Internal face, internal surface, inner side of the fluid line  400   
           410  Fluid path on the fluid line  400  or on/in internal face  404   
           412  Opening of the fluid path  310  on the piston  300   
           422  (Internal) recess, internal recess 
           426  Groove, facet, longitudinal groove, longitudinal facet, recess 
           500  Injector body, injector housing with high-pressure line 
           502  to nozzle chamber  102   
           502  High-pressure line/bore fluidically connected to nozzle chamber  102  through the control assembly  20   
           504  Leakage port 
           510  Actuator, piezo actuator, electromagnetic actuator 
           512  Base plate of the actuator  510 , preferably with actuation projection for transmission pin  214