Abstract:
The invention concerns an injector for the injection of fuel into the combustion chambers of combustion engines. Inside an injector housing ( 9 ) is located a nozzle needle ( 14 ), which is surrounded by a nozzle chamber ( 18 ). The nozzle needle ( 14 ) is moveable back and forth within the injector housing, and is aligned by the guiding sections ( 16, 22 ) inside the injector housing ( 9 ). A thick spring ( 11 ) pressed the nozzle needle against the injector ( 14 ) a ring canal ( 23 ) is formed between injector housing ( 9 ) and nozzle needle ( 14 ) and a conical section ( 33 ) of said nozzle needle ( 14 ) follows in the direction towards the seat ( 30 ).

Description:
BACKGROUND OF THE INVENTION 
     This invention concerns fuel injection systems for direct injection combustion engines, in general, and in particular, those fuel injection systems which contain valve bodies that are moveable back and forth across an operational unit in a vertical direction in the injector housing. The start of injection and the amount of fuel injected are adjusted for the injectors which are admitted into the top of the cylinder area, projecting into the individual combustion spaces of the combustion engine, and are maintained during the operation of the combustion engine. The injectors are, as a rule, fitted into the cylinder top area of the combustion engine without major structural alteration. 
     DE 197 01 879 A1 discloses a fuel injection system for fuel engines. The arrangement known from this reference involves a high pressure pump, which fills a fuel-fillable common high pressure container (Common Rail) with fuel. The same high pressure container is connected with an injection valve which projects into the combustion area of the engine to be fueled, the opening and closing movements of which valves are controlled by an electrically operated control valve, whereby the control valve is formed as a 3/2-way valve, which is connected to a high pressure canal flowing into an injector opening of the injector valve, by means of the injector conduit or a drainage conduit. Thereby, is provided at the control valve joint of the control valve a workspace hydraulically fillable with high pressure fuel, which is controllable for adjustment of the positioning of the control valve joint of the control valve into a drainage canal. 
     DE 198 35 494 A1 discloses a pump nozzle unit. This serves for the supply of fuel into a combustion space of direct injection combustion engines with a pump unit for the buildup of injection pressure and for the injection of the fuel across an injection nozzle into the combustion space. The teachings of this reference embrace, moreover, a control unit with a control valve which is formed as an outer opening A-valve, as well as a valve operational unit for control of the pressure buildup inside the pump unit. In order to provide a pump-nozzle unit with a control unit, which has a simple construction, is small in size and in particular has a short response time, it is suggested according to the present invention to form the valve operational unit as a piezoelectrically active unit. 
     SUMMARY OF THE INVENTION 
     With the configuration suggested according to the present invention of a nozzle needle of an injector for the injection of fuel into the combustion space of combustion engines, a slanted configuration can be formed for the course of the fuel injection throughout the cylinder path, and thereby the behavior of the fuel injection. The slant is formed between a control surface provided on the inside of the housing, which attaches to a control edge of the injector housing, and a conical area provided on the nozzle needle. On the side of the nozzle needle, the conical section is situated opposite the portion of the area of the borehole in the injector housing, in which the needle nozzle is moveable back and forth. 
     Above a constriction in the nozzle needle there is located an upper management section of the nozzle needle. Free surfaces are provided inside this upper management section, across which the fuel can flow from the nozzle space into which it enters under high pressure from the high pressure collecting area, in the direction of the point of the nozzle needle. In more advantageous manner, the management section of the nozzle needle provided by means of the mentioned free surfaces, defines a ring shaped canal. The ring shaped canal functions between a straight surrounding section of the nozzle needle and a front surface section of the wall of the housing, as a throttle element next to the lower end of the nozzle needle, which thanks to its conical formation likewise functions as a throttle element. Across the ring shaped canal which functions as a throttle element, there enters during a first partial stroke of the nozzle needle within the injector housing only a small volume of fuel into the combustion space of the combustion engine. In this manner, a continuous ignition delay can be set at the start of the injection operation up until complete development of the flame front in the combustion space. Through further elevation of pressure at the pressure stage of the nozzle needle in the nozzle space, the nozzle needle will be upwardly driven towards the effect of the thick spring, so as to produce during the further cylinder path of the nozzle needle, a gradual widening of the distance between the control surface provided in the wall of the housing and the conical area of the nozzle needle. The result is that from the start of the spraying, the effective ring shape canal is continuously widened during the further cylinder path of the nozzle needle and a greater volume of fuel can be transported. The increase in the amount of injected fuel obtainable by means of the conical surface of the nozzle needle is implemented first after a complete formation of the flame front in the combustion space, so that the ignition delay disappears and an increased volume of fuel will be sprayed at the right time into the combustion space of the combustion engine, namely when the thermodynamic conditions are optimal therefor. 
     An accurate prescription for the course of the pressure buildup during the injection phase depends upon the length of the slope of the conical area of the nozzle needle, furthermore on the angle of the pitched surface relative to the front surface, and upon the vertical cylinder path of the nozzle needle within the injector housing. 
     The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal section through a nozzle needle with a tooled slant, placed inside an injector housing in accordance with the present invention. 
     FIG. 2 is a magnified section from FIG. 1, showing the tooled slant formed on the nozzle needle, opposite a control surface inside of the housing. 
     FIG. 3 is a graph showing the timing for the course of the injection pressure for the needle nozzle in accordance with the present invention, taken relative to the cylinder path. 
     FIG. 4 is a magnified representation of the control edge and control surface of the inside of the housing, which lie opposite a pitched surface formed on the nozzle needle which is driven through the course of the injection pressure. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 of the drawings more closely illustrates a longitudinal section through a nozzle needle which is surrounded by an injector housing. 
     FIG. 1 shows an injector  8  for the injection of fuel into the combustion space of a combustion engine, which is connected to a high pressure collecting area 1 (Common Rail). The conduit stretching from high pressure collecting area 1 (Common Rail), which flows into nozzle chamber input  17 , passes through a 3/2-way valve  2 . This valve is controlled, as shown in this particular embodiment, by means of control chamber  3 , which receives fuel through a branch from the pressure conduit from high pressure collecting area 1 and an inflow choke  5  therefrom, which provides a control volume. A change in the pressure inside control chamber  3  can be carried out by means of a 2/2-way control valve  6 , which connects as seen with drainage conduit  7 . Additionally, an outflow choke  4  is associated with the pressure relief conduit of control chamber  3 . 
     Injector  8  substantially encloses the introduced nozzle needle  14 , which is admitted into a borehole in the injector housing  9 . The nozzle needle  14  is associated at its top surface  15  with a cone-shaped pressure piece  13 , The cone-shaped pressure piece  13  abuts on one side the thick spring  11 , provided as a spiral spring, which shores up the support element  10  provided at the top interior of injector housing  9 . Support element  10 , cone-shaped pressure piece  13 , as well as nozzle needle  14  are all constructed rotationally symmetric to the axis of symmetry  12 . Beneath the top area of needle nozzle  14 , which is formed as a first guide section  16 , there is located in injector housing  9  a nozzle chamber  18 , which is supplied with high pressure fuel from high pressure collecting area  1 , through 3/2-way control valve  2  and nozzle chamber input conduit  17 . Inside nozzle chamber  18  within injector housing  9 , the nozzle needle  14  is shaped with a pressure stage  19 . Pressure stage  19  brings about, upon supply of pressure into nozzle chamber  18  the driving nozzle needle  14  and therewith the release of injection hole  32 . The vertical cylinder pathway of nozzle needle  14  is schematically illustrated in the representation according to FIG. 1, by means of the double arrow next to axis of symmetry  12 . Beneath a constricted section of nozzle needle  14 , which is substantially enclosed by nozzle chamber  18  within injector housing  9 , below the nozzle chamber  18 . In order to make possible the flow of fuel entering nozzle chamber  18  to the conically formed nozzle needle point, there is disposed within the second guiding section  20 , below nozzle chamber  18  a free surface  42 . It is across free surface  42  that the high pressure fuel enters into the area of the borehole inside of injector housing  9 , which is limited on the nozzle needle side by constricted area  21 . 
     Beneath constricted area  21  there is located a ring-shaped extension of nozzle needle  14 , and a conical area  33 , which is embodied in the nozzle needle head. Below conical area  33  there follows a ring-shape chamber  28 , which is bounded on the housing side by a ring groove  35 , and on the nozzle needle side by a further constricted area  34  of the nozzle needle  14 . Below this ring chamber  28  the nozzle needle is shaped at its point side into a conical seat  29 , on which is formed seat diameter  30 . By means of seat diameter  30 , the point of nozzle needle  14  is driven against a seat formed by the wall  31  of injector housing  9 , and it is locked in place there by means of the effect of thick spring  11  and also the force of pressure adjusting through injection opening  32  to the upper end  15  of nozzle needle  14 . At injection opening  32 , the injector  8  configured in accordance with the present invention, illustrated by FIG. 1, projects into the combustion space of a combustion engine. 
     The illustration according to FIG. 2 shows the construction of the control surfaces inside of the housing, opposite the tooled slant of the nozzle needle. 
     In accordance with the representation of FIG. 2 one sees an enlarged section, including, beneath the second guiding section  20  and the constricted area  21  which follows on nozzle needle  14 , a control surface stretching from control edge  8 ′ provided inside of the housing, which forms a throttle place having variable cross-section opposite that section of the nozzle needle. The throttle cross-section varies, depending upon the path of the nozzle needle  14  inside of injector housing  9 . The control surface which follows control edge  8 ′ on the inside of the housing runs vertically downwardly and is formed by the wall of injector housing  9 . This wall is opposite a ring-shaped section of the nozzle needle, thereby defining a canal height  25  (h 1 ). The canal, formed between the ring-shaped area of nozzle needle  14  and the section of the control surface of injector housing  9  lying opposite, is designated by reference numeral  23 . The cross-sectional surface of canal  23  is designated by reference numeral  22 , which refers to the free canal surface and which forms a throttle place. Adjacent to the ring-shaped section of nozzle needle  14  which stretches across canal height  25  (h 1 ) there is associated a conical area  33  The conical area  33  opens in the direction of the point of nozzle needle  14 . Between the vertical of the downwardly stretching control surface adjacent to the control edge  8 ′ of injector housing  9  and the surface of the conical section of the needle nozzle  14  is defined an angle δ identified as  27 . After the conical section  33  of nozzle needle  14 , the axial extent of which is designated by reference numeral  41  (h 3 ), a ring groove  34  is provided on the nozzle needle  14 . The ring groove  34  forms, according to the representation of FIG. 2, along with ring groove-shaped section  35  of the interior wall of injector housing  9 , a ring chamber. Following chamber  28  one sees a throttle place with variable cross-section, through which flows the fuel as it passes conical seat  29  of nozzle needle  14  along the direction towards the nozzle point; and injector opening  32 . 
     The length of the control surface associated beneath control edge  8  on the inside wall of injector housing  9  is designated by reference numeral  26 , and corresponds approximately to the canal height  25  (h 1 ) and the extent of conical section  33 , parallel to the axis of symmetry  12  of nozzle needle  14 . 
     FIG. 3 illustrates the adjusting of the course of the injection pressure with the nozzle needle configured in accordance with th present invention, always taken across the piston path of the nozzle needle. 
     Reference numeral  36  designates the course of the injection pressure, as a function of the cylinder path  37  of the nozzle needle  14 . In the diagram according to FIG. 3, one sees represented the pressure course characteristics  38  and  39 . Indeed, depending upon the selected axial length of control surface  22  beneath control edge  8 , canal height  25  and the axial extent of conical section  33  in the direction of the axis of symmetry  12  of nozzle needle  14 , and depending upon selected angle  27  of the conical section  33  relative to the vertically running borehole inside injector housing  9 , one obtains a flatter injection pressure curve  39  or a steeper injection pressure curve  38 . One sees from the represented course of pressure characteristics  38  and  39 , that initially an asymptotically running pressure curve is produced, so long as control edge  8  and the area of canal height  25  cover each other, that is, until the start of the vertical driving phase of nozzle needle  14  against the effect of thick spring  11 . During this phase, that is a first partial path of nozzle needle  14  inside injector housing  9 , the throttle cross-section remains constant until it first begins to increase as control edge  8  overlays the start of the conical section of the nozzle needle. During this further partial path, across piston length  41 , that is the axial extent of nozzle needle  14  corresponding to the conical section, the throttle cross-section is continuously widened upon further vertical movement of the nozzle needle against the effect of thick spring  11 . Depending upon the angle of incline  27 , the cross-section increases, whereby a faster obtaining of a high pressure level according to the dashed line (course of injection pressure  38  in FIG. 3) can be accomplished. In this area of the graph, designated by reference numeral  41 , in which the throttle cross-section increases continuously, one sees a steeper pressure slope section, so that the maximum pressure is reached more quickly. Indeed, according to the selected axial extent  41  (h 3 ) of conical section  33 , as well as the selected slant angle  27 , the increase in pressure according to FIG. 3 can advantageously be adjusted to follow either pressure course characteristics  38  or  39 . Axial extent  26  (h 2 ) of the control surface provided on the inside of the housing corresponds at least to both partial path  25  and partial path  41 , during execution of the driving of nozzle needle  14  against the effect of thick spring  11 . 
     The representation according to FIG. 4 is an enlarged display of the control edge on the inside of the housing, which is located across the inclined surface formed on the nozzle needle, throughout the buildup of the injector pressure. The total pathway  40  of nozzle needle  14  is in advantageous manner so selected that it is always either equal to partial path  25  (h 1 ) plus partial path  41  (h 3 ) or, both partial path  25  and partial path  41  are so selected that their sum is smaller than the total pathway  40  of nozzle needle  14 . With the nozzle needle  14  inserted into injector housing  9 , configured in accordance with the present invention, one can produce not only an increase in the course of pressure, but through adjustment of the ring canal diameter  23  as well as the partial pathways  25  and  41  on the side of the nozzle needle, and also the length of the control surface associated with control edge  8 ′ on the side of the housing, the pressure characteristics of the pressure buildup can be adjusted. The opening pressure of nozzle needle  14  can be influenced by the configuration of pressure stage  19 , which is formed on the nozzle needle section in the area of thee enclosed nozzle chamber  18 . The opening pressure of the nozzle needle  14  is determined by the dimensioning of thick spring  11 , which is provided within injector housing  9  above the top surface  15  of nozzle needle  14 . In connection therewith, it makes no difference whether the injector is directly controlled across a 3/2 way valve  2  or is controlled by means of an operational unit, for example a piezoactive or a magnetic valve. 
     With the solution suggested according to the present invention, one can obtain a control of the injection pressure not only during a partial path range of the injector but also throughout its entire cylinder pathway running in a vertical direction. In so doing, depending upon configuration of the conical area  33  as well as the axial dimension of control surface  22  within injector housing  9 , one can arrive at the most discriminating degree of customer adjustment of the injection characteristics, be it for direct-injection combustion engines in personal motor vehicles or in commercial vehicles, taking into account a full range of fine tuning. 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 
     While the invention has been illustrated and described as embodied in a pressure controlled injector with optimized injection characteristics throughout the cylinder path, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from that the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. 
     What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.