Abstract:
A gas injector for the direct injection of gaseous fuel into a combustion chamber of an internal combustion engine, including a valve seat, a valve needle, which in response to a lift releases a first cross-sectional area at the valve seat, and a gas control region, which is situated at the valve needle and defines a second cross-sectional area together with a component surrounding the valve needle, and in response to a lift, a change in the first cross-sectional area at the valve seat differs from a change in the second cross-sectional area at the gas control region.

Description:
RELATED APPLICATION INFORMATION 
       [0001]    The present application claims priority to and the benefit of German patent application no. 10 2014 200 756.9, which was filed in Germany on Jan. 17, 2014, the disclosure of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a gas direct injector for the direct injection of gaseous fuel, such as natural gas, into a combustion chamber of an internal combustion engine. 
       BACKGROUND INFORMATION 
       [0003]    Apart from the frequently used liquid fuels, the use of gaseous fuels, such as natural gas or hydrogen, has been increasing over the past few years as well. However, the known injectors for liquid fuels are only conditionally suitable for such gaseous fuels, since gaseous fuels have different energy densities and volumes than liquid fuels. To ensure that internal combustion engines operated in this manner do not consume too much fuel, it is necessary to inject the most precise gas quantities possible in each injection. In the future, to save fuel, it will additionally be necessary to carry out one or more injection process(es) as well. Apart from the requirement of injecting a certain maximum quantity within a predefined period of time, it must also be possible to meter defined minimal gas quantities in a precise manner. The gas injector also needs to seal with respect to the combustion chamber between different injections.  FIG. 1  schematically illustrates an example of a known gas injector  1 , in which an outwardly opening valve needle  3  sits on a valve seat  2  inside a housing  5 .  FIG. 1  shows the closed state of the injector.  FIG. 2  schematically shows a diagram of a characteristic of the effective overall opening cross-section A across lift H. Here, a linear characteristic comes about both for smaller lifts and for large lifts H, as long as the released annular cross-sectional area at the valve needle constitutes the smallest cross-section. Accordingly, a constant cross-sectional area A max , which is independent of lift H, results as soon as the annular gap between nozzle needle  3  having radius R 2  and the outer contour (radius R 1 ) at valve seat  2  of the gas supply of the injector represents the smallest cross-section. For this reason the curve in the diagram of  FIG. 2  is horizontal in the end region up to maximum lift H max . 
         [0004]    A conflict in goals between the metering of minimal quantities and a maximally desired quantity per injection cycle exists in the configuration of gas injectors. Because of the relatively low density of gaseous fuels, high volumes must be injected within a short period of time at space requirements that are comparable to an injector for liquid fuels. To do so, a gas injector should be able to release large cross-sections as rapidly as possible at a given lift. As a result, the concept of the gas injector shown in  FIGS. 1 and 2  has the steepest possible cross-sectional characteristic over the lift. However, this makes it difficult to meter minimal quantities, and multiple injections, in particular, are impossible to realize. 
       SUMMARY OF THE INVENTION 
       [0005]    In contrast, the gas injector according to the present invention for the direct injection of gaseous fuel into a combustion chamber of an internal combustion engine, having the features described herein, has the advantage of allowing also the metering of minimal gas quantities without any problems. In particular a multi-injection of fuel during an injection cycle is possible in this manner. In the present invention, this is achieved by developing a gas control region at a valve needle, which together with a component that surrounds the valve needle defines a second cross-sectional area. A change in the second cross-sectional area in response to a lift differs from a change in a first cross-sectional area at a valve seat during the opening operation of the valve needle. As a result, a second cross-sectional area, through which the gaseous fuel must flow until it reaches the actual valve seat, is able to be defined by the selection of a geometry. The second cross-sectional area varies across the lift of the valve needle and provides a further control curve for the gas quantity to be injected. 
         [0006]    The further developments of the present invention are also described herein. 
         [0007]    The second cross-sectional area at the gas-control region may be constant at the start of a lift of the valve needle up to a predefined lift length. This makes it possible to easily inject a small gas quantity at small lifts, since the first cross-sectional area at the valve needle becomes continually larger at the start of the lift. 
         [0008]    Furthermore, the gas-control area may have a control edge, which has the form of a ring. This makes for an especially simple control of the gas quantity by way of geometry. In particular, the annular control edge may have a larger diameter than a diameter of the valve seat. 
         [0009]    According to an alternative development of the present invention, the gas-control region has a control edge, which is configured in the form of a star or blossom and includes a multitude of jags or waves (petals). A long control edge, in particular, is realizable in this manner without enlarging the cross-sectional area or the radius of the housing in its respective dimensions. The geometric development of the control edge with star-shaped jags also makes for a relatively easy adaptation to different specifications of injectors, in that, for example, individual jags or jagged regions are removed, so that the cross-sectional conditions in the gas control region are able to be modified rapidly. 
         [0010]    In a further manner, the gas control region has continuous recesses, or the gas control region has recesses at its outer periphery, such as removed jags, bulges or the like. This measure, as well, makes it possible to achieve an individual adaptation of the second cross-sectional area at the gas control region in a relatively uncomplicated manner. 
         [0011]    The component that surrounds the valve needle especially may be a housing of the gas injector. This makes it possible to realize an especially compact and slender structure. 
         [0012]    According to a further development of the present invention, the gas injector includes an additional sealing element, which is disposed in the gas control region. The sealing element may be situated at the control edge of the valve needle or situated on the component that surrounds the valve needle. The use of the additional sealing element makes it possible to realize a pre-valve in the gas control region, so that additional, more reliable sealing of the gas valve is possible. Since the actual valve seat at which the valve needle is sealing or releasing the first cross-sectional area is exposed to the relatively high temperatures at the combustion chamber, the use of the sealing element at the gas control region, for example, makes it possible to use even materials that would not be able to withstand the high temperatures at the combustion chamber. The sealing element may especially be an elastomer. 
         [0013]    A cross-sectional area for ejecting gas at the valve seat of the gas valve may be in a range of 2 mm 2  to 6 mm 2 . This ensures that gas quantities of sufficient size are able to reach the combustion chamber via the first cross-sectional area during a valve lift. A diameter of the annular control edge furthermore may be in a range of 7 mm 2  to 20 mm 2 . 
         [0014]    According to a further development of the present invention, an exiting gas mass flow is within a range of 5 to 15 g/s. 
         [0015]    Furthermore, the gas injector may include a piezo actuator or, alternatively, a magnet armature as actuator. The present invention in particular also allows the use of magnetic actuators, so that very small lifts, and thus very small injection quantities, are realizable, despite the use of magnetic actuators. 
         [0016]    The valve needle especially may be an outwardly opening valve needle. 
         [0017]    The gas injector especially may be used for the direct injection of gaseous fuel into a combustion chamber of internal combustion engines of vehicles. As an alternative, the gas injector may also be used in stationary gas motors. 
         [0018]    Furthermore, the gas injector according to the present invention has a relatively simple and robust configuration, so that especially also high gas pressures that are considerably higher than pressures in fluid fuel injection systems, for example, do not cause damage to the injector. 
         [0019]    In addition, the present invention relates to a gas-operated internal combustion engine, which includes a gas injector according to the present invention. 
         [0020]    Exemplary embodiments of the present invention are described in detail below, with reference to the accompanying drawing. Identical or functionally equivalent parts are designated by the same reference numerals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  shows a schematic sectional view of a gas injector according to the related art. 
           [0022]      FIG. 2  shows a diagram, which represents the effective cross-sectional area A at the valve seat that opens in response to a lift H of a valve needle of the gas injector, according to the related art. 
           [0023]      FIG. 3  shows a schematic sectional view of a gas injector according to a first exemplary embodiment, in the closed state. 
           [0024]      FIG. 4  shows a schematic illustration of a diagram which shows the effective opening area A across a lift H of the valve needle in the first exemplary embodiment. 
           [0025]      FIGS. 5 and 6  show different open positions of the gas injector of  FIG. 3 . 
           [0026]      FIG. 7  shows a schematic sectional view along line VII-VII of  FIG. 3 . 
           [0027]      FIGS. 8 ,  9  and  10  show schematic sectional views of alternative exemplary embodiments of a gas injector. 
           [0028]      FIG. 11  shows a schematic sectional view of a gas injector according to a second exemplary embodiment of the present invention. 
           [0029]      FIG. 12  shows a schematic sectional view along line XII-XII of  FIG. 11 . 
           [0030]      FIGS. 13 and 14  show schematic sectional views of alternative exemplary embodiments. 
           [0031]      FIG. 15  shows a schematic sectional view of a gas injector according to a third exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    In the following text, a gas injector  1  according to a first exemplary embodiment of the present invention is described in detail with reference to  FIGS. 3 through 7 . 
         [0033]    Schematically illustrated gas injector  1  includes a valve needle  3 , which seals at a valve seat  2  configured on a housing  5 . Valve seat  2  has a radius R 3 . 
         [0034]    In addition, gas injector  1  has an inner gas control region  4 , which includes a control edge  40  which radially projects in the outward direction from a base body of valve needle  3 . Inner gas control region  4  has a cylindrical lateral surface  41 , which is parallel to an inner lateral surface  51  of housing  5 . This provides an annular gap  42  between housing  5  and inner gas control region  4 . Control edge  40  has a radius R 4 . Annular gap  42  can be gathered from  FIG. 7 , in particular. 
         [0035]    If an actuator (not shown) then moves valve needle  3  in the direction of arrow A, valve needle  3  lifts off from valve seat  2 . As can be gathered from  FIG. 4 , a first cross-sectional area at valve seat  2  that increases at a constant gradient across a very small lift length H 1  is released in the process. This cross-sectional area is denoted by A 1  in  FIG. 4  and corresponds to the cross-sectional area provided by annular gap  42 . This cross-sectional area A 1  remains constant across further lift H 2 , which corresponds to the height of lateral surface  41  of inner gas control region  4 , since inner gas control region  4  retains the constant annular gap cross-section despite the fact that the first cross-sectional area at valve seat  2  becomes ever larger with increasing lift. 
         [0036]    As soon as the valve needle attains the position illustrated in  FIG. 5 , the cross-sectional area at gas control region  4  enlarges continuously. This results in a rising effective cross-sectional area A in the region between lift length H 2  and H 3  in the diagram from  FIG. 4 , until first cross-sectional area at the valve seat is as large as the second cross-sectional area at inner gas control region  4 . This state is illustrated in  FIG. 6  and attained in  FIG. 4  at lift length H 3 . 
         [0037]    In a further lift, the effective opening cross-sectional area that opens further at the valve seat is therefore no longer delimited by inner gas control region  4 , but solely by the geometry at valve seat  2 . As a result, starting with lift length H 3 , the curve shown in  FIG. 4  corresponds to the curve having a constant gradient of the related art shown in  FIG. 2 , so that large gas quantities are injectable as well. 
         [0038]    Downstream from inner gas control region  4  in the flow direction, gas injector  1  has a relatively large space  6 , which has a large cross-section, in particular, so that once a predefined lift has occurred at inner gas control region  4 , the inner gas control region no longer has an effect on the overall cross-sectional area for the injection of fuel. 
         [0039]    According to the present invention, additional control edge  40  at inner gas control region  4  is therefore able to make available a precision-control region for minute gas quantities, which ranges up to a lift slightly beyond lift length H 2  (compare  FIG. 4 ). According to the present invention, by providing inner gas control region  4 , influencing of effective cross-sectional area A is therefore possible, as a result of which it is also possible to supply only small gas quantities at small lifts. Starting with a certain lift length, which in particular is greater than lift length H 3 , it is nevertheless possible to supply a large injection quantity as required for gaseous fuels, since effective cross-sectional area A then depends solely on the geometry at valve seat  2 . As a result, the gas injector according to the present invention can also satisfy the requirement that large cross-sections have to be released as rapidly as possible at a given lift in order to be able to inject large fuel gas quantities. This is important especially because gaseous fuels have a lower energy content at the same volume in comparison to liquid fuels. 
         [0040]    The present invention furthermore also makes it possible to provide a multi-stage and repeated injections, and minimal quantities, in particular, are able to be metered precisely as well. 
         [0041]      FIGS. 8 through 10  show alternative developments of inner gas control region  4 ; in  FIG. 8 , for instance, planar side surfaces  44  are configured, which define the flow rate in the region of the lift between lift lengths H 1  and H 2 . Precisely four planar side surfaces  44  are provided in this context, two planar side surfaces  44  lying across from each other in each case. 
         [0042]    In  FIG. 9 , a multitude of angular recesses  45  are provided at the outer periphery of gas control region  4  of valve needle  3 , which extend in the axial direction X-X. 
         [0043]    A multitude of cylindrical, axial through recesses  46  are configured in gas control region  4  of valve needle  3  in  FIG. 10 . 
         [0044]    As these examples from  FIGS. 8 through 10  illustrate, it is therefore possible to develop a control surface in an individual manner in a relatively uncomplicated manner through different geometry selections at gas control region  4 , so that, for example, different gas injectors are easily able to be supplied for different vehicle manufacturers, on the basis of a fundamental concept. 
         [0045]      FIGS. 11 through 12  show a gas injector  1  according to a second exemplary embodiment of the present invention. In contrast to the first exemplary embodiment, inner gas control region  4  in the second exemplary embodiment is formed differently. As can be gathered from  FIG. 12 , inner gas control region  4  is provided in the form of a star which has a multitude of points  47 . Similar to the first exemplary embodiment, the lateral region of inner gas control region  4  is once again parallel to an inner wall  51  of housing  5 , which has a correspondingly formed star-shaped recess for inner gas control region  4 . 
         [0046]    As illustrated in  FIGS. 13 and 14 , here, too, it is possible to provide different cross-sectional areas by cutting the tips of points  47  ( FIG. 13 ) or by providing through openings  46  ( FIG. 14 ). 
         [0047]      FIG. 15  shows a gas injector  1  according to a third exemplary embodiment of the present invention. Gas injector  1  of the third exemplary embodiment additionally also has an elastomeric sealing element  7 , which is disposed at housing  5 . A step  52  is provided on housing  11  for this purpose. Sealing element  7  together with a sealing surface  8  at the inner gas control region  4  forms a pre-valve.  FIG. 15  shows the closed state of the valve, in which both the pre-valve and the main valve at valve seat  2  are closed. This makes it possible to use an elastomeric sealing element  7  for sealing gas injector  1 , which otherwise would not be usable in gas direct injectors due to the direct placement at the combustion chamber for the direct injection of the gas into the combustion chamber. In addition, because of the use of sealing element  7 , gas injector  1  provides additional safety as regards the sealing. The cross-sectional area changes in response to a lift at the first and second cross-sectional area correspond to the changes in the first exemplary embodiment.