Abstract:
The invention relates to a fuel injector comprising a nozzle retainer or an injector body, a valve body and a nozzle body, in which a preferably needle-shaped injection valve member is arranged to be vertically movable, said member releasing or closing at least one injection port leading to a combustion chamber of an internal combustion engine depending on the pressure relief of or the pressure load on a control chamber. The invention is characterized in that a valve comprising a preferably ball-shaped valve element is arranged in the nozzle retainer or in the injector body for the pressure relief of the control chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP2008/064831 filed on Oct. 31, 2008. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     In modern internal combustion engines, in particular Diesel engines, injection systems are used in which a high-pressure pump puts the fuel at a high pressure level. The fuel acts on a high-pressure reservoir body (common rail), which when the engine is in operation is constantly under pressure or in other words is subjected to a system pressure level generated by the high-pressure pump. High-pressure lines that ensure the supply of fuel to the engine cylinders branch off from the high-pressure reservoir body. Via fuel injectors, the fuel that is delivered via the high-pressure lines is injected into the combustion chamber of the cylinders of the engine. 
     2. Description of the Prior Art 
     In common rail injection systems, the injection event into the combustion chambers of the engine is uncoupled from the pressure generation in the high-pressure reservoir body (common rail). As a result, the instant and quantity of fuel injection can be controlled by engine electronics. This makes an injection adapted to the particular engine load possible. In typical applications, a system pressure of at least 1800 bar is generated in the high-pressure reservoir body (common rail); even high pressures above 2000 bar can be generated. By means of common rail injection systems, a plurality of injections per work cycle can be achieved. Typically, this results in a preinjection, a main injection, and a postinjection. 
     The control of the injection event is effected with the aid of an electrical signal, which is generated by the control unit of the engine. The electrical signal serves to trigger a solenoid valve for actuating the fuel injector. This solenoid valve, via suitable hydraulics, regulates the motion of a preferably needle-shaped injection valve member, which with its tip opens or closes at least one injection opening into the combustion chamber of the engine. The injection event is initiated by actuation of the solenoid valve, as a result of which a fuel-filled control chamber is pressure-relieved by actuation of the preferably needle-shaped injection valve member. Because of the pressure relief of the control chamber, the preferably needle-shaped injection valve member moves upward, and as a result, at the tip of the injection valve member, injection openings embodied in the nozzle body are opened. 
     In the prior art, the solenoid valve exists in many different structural forms, as for example in German Patent Disclosure DE 196 50 865 A1. In a variant, a spherically embodied valve element is used, which is disposed at the upper end of the fuel injector and can be moved longitudinally of the fuel injector axis, which coincides with the axis of the injection valve member. In the closed state, the spherically embodied valve element seals off a conically polished valve seat. 
     As a further variant, the solenoid valve can also be placed in the lower region of the fuel injector, particularly in the injector body of the fuel injector. European Patent Disclosure EP 0 740 068 B1 discloses one such variant of a fuel injector. A valve member there is guided in a valve body, which is sealed off from the fuel that is at high pressure. In this way it is ensured that the fuel at high pressure does not exert any forces on the valve member. Typically, the axis of motion of the valve member, in such a variant, is offset laterally from the axis of motion of the injection valve member. Such a fuel injector is substantially more expensive to produce than a fuel injector provided with a spherically embodied valve member. 
     SUMMARY OF THE INVENTION 
     The present invention realizes a fuel injector with a valve that has a spherically embodied valve element, and this valve is placed directly in the injector body of the fuel injector. The valve is sturdy and has withstood the test of time. In a preferred feature of the present invention, the valve makes do without guidance of an armature or a pressure equilibrium. Thus this valve is very inexpensive. 
     The valve with the spherically embodied valve element is prestressed by a valve spring and is pressed into a closing position. When current is supplied to a magnet, an armature unit is attracted, counter to the action of the valve spring, and opens an outlet conduit from the control chamber. A control quantity flows out from this chamber, so that the preferably needle-shaped injection valve member moves into the control chamber and opens at least one injection opening on the end of the fuel injector toward the combustion chamber, so that fuel can be injected into the combustion chamber of the engine. 
     In the state of repose, the valve spring, via the armature, presses the spherically embodied valve element into a valve seat, which for example is embodied conically. In this state, the valve seat is sealed off by the closing force acting in the vertical direction as a result of the valve spring. The force exerted by the valve spring, in the state of repose, exceeds a contrary force generated by the system pressure in the control chamber. 
     The control chamber communicates with a high-pressure line via a first throttle restriction (inlet throttle restriction) and with the valve seat of the spherically embodied valve element via a second throttle restriction (outlet throttle restriction). The upper end of the preferably needle-shaped injection valve member protrudes into this control chamber. The preferably needle-shaped injection valve member is disposed vertically movably along a second axis, and this second axis extends parallel to the first axis of the valve spring. In the state of repose, fuel at system pressure is located in the control chamber and is delivered from the high-pressure line via the inlet throttle restriction. The force exerted by the fuel at system pressure on the preferably needle-shaped injection valve member ensures that the preferably needle-shaped injection valve member is not moved all the way into the control chamber. In this state, the preferably needle-shaped injection valve member closes at least one injection opening located at its tip. The fuel delivered to this injection opening via the high-pressure line can accordingly not be injected into the combustion chamber of the engine. 
     In an embodiment of the present invention, the armature unit, in particular the armature plate, is joined together from one inner component and one outer component. The inner part and the outer part are made from two different materials, and the material for the outer part is selected in accordance with magnetic properties. The material for the inner part of the armature unit is selected in accordance with mechanical requirements in view of hardness and machinability in the vicinity of the valve element as well as with regard to the mechanical requirements of the stroke stop. The two parts of the armature may be joined to one another positively or nonpositively. The armature is not guided in the valve body of the valve; instead, the position of the armature in the closed state of the valve results from the fact that the spherically embodied valve element is aligned with the valve seat, and the armature in turn is aligned with the spherically embodied valve element. In a variant embodiment, the armature may also be embodied of a single material as a one-piece component. It is equally well possible to provide a closing element receptacle, for the closing element that for example can be embodied spherically, on the armature unit. As a result, a greater axial offset of the armature unit relative to the valve seat can be compensated for. This variant, that is, the use of a closing element guide, can be combined with the armature that can be embodied as either in one piece or, as sketched above, in two parts. The armature is guided in the magnet core of the valve with a slight radial play, so that a virtually perpendicular orientation of the armature plate relative to the face end of the magnet is ensured. 
     In further variant embodiments what is proposed according to the invention, the possibility exists of locating the valve seat in the interface plane between the injector body and the valve body. This disposition of the valve seat has advantages upon assembly of the fuel injector. In one embodiment, the solenoid valve assembly can be aligned via a spacer sleeve on the valve body or can be surrounded in a sleeve (cartridge) that receives the entire electromagnet valve assembly. The electromagnet and the sleeve can be joined together nonpositively or positively and are disposed as a preassembled unit in the injector body of the fuel injector proposed according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are described in further detail in the ensuing description in conjunction with the drawings, in which: 
       Exemplary embodiments of the invention are described in further detail in the ensuing description. 
         FIG. 1  shows a fuel injector corresponding to the prior art, with a conventional injection valve member; 
         FIG. 2  shows an embodiment according to the invention of the fuel injector, with a valve that has a spherically embodied valve element; 
         FIG. 3  shows an enlarged detail of  FIG. 2 ; 
         FIG. 4  shows a variant of the fuel injector, with a valve that is actuated via a one-piece armature; 
         FIG. 5  shows a variant of the fuel injector of the invention, with a valve which in addition to the one-piece armature has a closing element guide; 
         FIG. 6  shows a variant of the fuel injector of the invention, having a valve that is actuated by an armature running in a guide; 
         FIG. 7  shows a variant of the fuel injector of the invention, having a valve that is fixed via an armature that is aligned via spacer sleeves in the valve body; and 
         FIG. 8  shows a variant of the fuel injector of the invention, having a valve that includes an electromagnet and a magnet sleeve joined to the electromagnet positively and nonpositively. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , a fuel injector corresponding to the prior art is shown, which has a conventional valve needle. 
     An injector body or “nozzle holder”  10  includes a high-pressure line  40 , which is filled with fuel, for instance Diesel fuel. The nozzle holder  10  further includes a magnet  110 , which is controlled via an electrical connection  120 . The magnet  110  is connected to a valve seat  130  and an injection valve member  100 . If an electric current is flowing through the magnet  110 , then the injection valve member  100  moves along a first axis and uncovers the communication with a control chamber  330 . In this way, the fuel located in the control chamber  330  can flow out through the valve  100  and a suitable connection. As a consequence of the fuel outflow from the control chamber  330 , the pressure in the control chamber  330  decreases. 
     In the lower part of the fuel injector there is a nozzle body  60 , which includes a preferably needle-shaped injection valve member  70  to which fuel is delivered via the high-pressure line  40 . To that end, there is a nozzle chamber  50 , which is filled with fuel, in the nozzle body  60 . A hollowed-out area  90  in the body of the injection valve member  70  is located in the vicinity of the nozzle chamber  50  and leads to a vertical reciprocating motion of the injection valve member along a second axis, which as a rule is disposed vertically, if the hydraulic force relationships vary. The hollowed-out area  90  serves to conduct fuel from the nozzle chamber  50  between the needle-shaped injection valve member  70  and the nozzle body  60 . The preferably needle-shaped injection valve member  70  continues to be closely guided in the nozzle body  60  in the vicinity of the hollowed-out area  90 . 
     The injection event is tripped in that the engine control unit, via the electrical connection  120 , sends a current through the magnet  110 , so that the valve member  100  opens up the communication with the control chamber  330  and thus reduces the hydraulic pressure in the control chamber  330 . In this way, the injection valve member  70  moves into the control chamber  330  and uncovers at least one injection opening  80  on the end toward the combustion chamber of the fuel injector, as a result of which fuel emerges from the at least one injection opening  80  and, in the event of sufficiently high pressure in the cylinder, is atomized. A clamping nut  25  ensures a positive fixation of the fuel injector on the cylinder head of the internal combustion engine. 
     In  FIG. 2 , the fuel injector of the invention is shown, with a valve including a spherical closing element  200 , which is used instead of the valve member  100  of  FIG. 1  that is used in the prior art. 
     The injection of the fuel, which is at system pressure, via a high-pressure line  40  is effected, as in the prior art, as a function of the position of a preferably needle-shaped injection valve member  70 . Analogously to the prior art, the injection event is initiated by feeding an electric current into a magnet  110 . In the fuel injector of the invention, the valve including the spherically embodied valve element  200  and the magnet  110  is seated inside the injector body  10 . Conversely, the valves used in the prior art are used only in the upper part of an injector body of the fuel injector, typically above a nozzle body. 
     In  FIG. 3 , an enlarged detail of the lower portion of the fuel injector of  FIG. 2  is shown. 
     Via the high-pressure line  40 , the fuel at system pressure is delivered. The high-pressure line  40  extends with a lateral offset from the axis of the nozzle holder  10  and extends through the valve body  30 . In the valve body  30 , the high-pressure line  40  forks. A first portion of the high-pressure line  40  extends through a cross-sectional constriction  310 , which is called a D throttle restriction and has a pressure-reducing effect. If the preferably needle-shaped injection valve member  70  is open and for terminating the injection the valve is closed, and the control chamber  330  is subjected to system pressure, then system pressure also prevails below the needle-like injection valve member  70 . The needle-like injection valve member  70  would for that reason, because of the action of a nozzle spring  335 , close very slowly. The cross-sectional constriction  310  called a D throttle restriction reduces the pressure below the needle-like injection valve member  70 , so that a greater hydraulic force is created, which markedly accelerates the closure of the preferably needle-shaped injection valve member  70 . 
     A further segment of the high-pressure line  40  extends on the other side of the cross-sectional constriction  310  and discharges into the nozzle chamber  50 . The shape, size and position of the nozzle chamber  50  can vary depending on the application; typically, the nozzle chamber  50  is disposed in the upper part of the nozzle body  60  as in  FIG. 2  and forms a closed ring around the injection valve member  70 . 
     A second line segment, branching off from the high-pressure line  40  after it forks, extends through an inlet throttle restriction  320 , which discharges into a control chamber  330 . The preferably needle-shaped injection valve member  70  protrudes with its upper end partway into the control chamber  330 , in the state of repose. The control chamber  330  also receives fuel that in the state of repose is at system pressure. The pressure of the fuel in the control chamber  330  compensates for the pressure generated by the fuel in the nozzle chamber  50 , so that the preferably needle-shaped injection valve member  70  in  FIG. 2  seals off the at least one injection opening  80  in  FIG. 2 . In this way, in the state of repose, no fuel can emerge from the at least one injection opening  80  and reach the combustion chamber of the cylinder. 
     Communicating with the control chamber  330  is an outlet throttle restriction  340 , which is provided in an outlet conduit  341  that discharges at an orifice  350  below the valve seat  342 . The spherically embodied valve element  200  and the orifice  350  form the valve seat  342 . The orifice  350  in this application is designed conically, so that a closing element  200  that is embodied spherically for instance and is seated in the orifice  350  seals off this orifice completely. In this way, in the position of repose, no fuel can emerge from the orifice  350  of the outlet conduit  341 . 
     In a preferred feature of the present invention shown in  FIG. 3 , above the spherical valve element  200  is an armature unit  352  with an inner armature part  370  which in the outset state as a result of the position of the spherically embodied valve element  200  is aligned relative to the valve seat  342 . An outer armature part  360  of the armature unit  352  laterally defines the inner armature part  370  and is joined, for instance by positive engagement, to the inner armature part  370 . In a preferred feature of the present invention, the armature unit  352  formed of the inner armature part  370  and the outer armature part  360  requires no guidance in the nozzle body  60 . Hence this valve is economical. 
     In the state of repose, a valve spring  380  exerts a closing force on the inner armature part  370  of the armature unit  352  and on the spherically embodied valve element  200 , along a first axis of motion. By means of this force, the spherically embodied valve element  200  is press-fitted with the aid of the inner armature part  370  into the valve opening  350 . The magnet  110 , pressed in the direction of the orifice  350  via a prestressing element  390 , is activated at the onset of the injection event by an electric current. As a result, the armature unit  352  is attracted, counter to the action of the valve spring  380  that acts in the closing direction. The orifice  350  of the outlet conduit  341  opens, and the control chamber  330  is pressure-relieved as a result of diversion of a control quantity. 
     By means of the orifice  350  opened during the injection event, the fuel can now escape from the control chamber  330 , so that the pressure in the control chamber  330  drops. Because of the lesser pressure in the control chamber  330 , the preferably needle-shaped injection valve member  70  moves into the control chamber  330 . In the process, the injection valve member  70  executes a motion along a second axis, which extends offset from and parallel to the first axis of the valve spring  380 . As a result of this motion of the preferably needle-shaped injection valve member  70 , the injection valve member  70  on its lower end uncovers the at least one injection opening  80  and enables the injection of fuel into the combustion chamber of the engine. 
     It can be seen from the view in  FIG. 3  that the armature unit  352  is constructed in two parts and includes an outer armature part  360  and an inner armature part  370 . In the variant embodiment shown in  FIG. 3 , the outer armature part  360  and the inner armature part  370  are made from two different materials. The material from which the outer armature part  360  is made can be selected for its magnetic properties. The material from which the inner armature part  370  of the armature unit  352  is made is selected to take mechanical requirements into account. With regard to the mechanical requirements, the hardness and machinability in the vicinity of the spherically embodied valve element  200  can be named, as well as the hardness with which stroke stops should be embodied. The two armature parts  360  and  370  of the armature unit  352  can be joined together by positive or nonpositive engagement. The armature unit  352  in the embodiment in  FIG. 3  has no guide in the valve body of the valve; in the closed state or in other words the state of repose of the fuel injector, the position of the armature unit  352  is due to the fact that the preferably spherically embodied closing element  200  is aligned with the valve seat  342  of the valve body  30 , and the armature unit  352  is in turn aligned with what here is the spherically embodied valve element  200 . 
     In a further variant of the fuel injector of the invention, instead of a two-piece armature unit  352 , including an inner armature part  370  and the outer armature part  360  in  FIG. 3 , a one-piece armature  400  is used.  FIG. 4  shows the one-piece armature  400  in an enlarged detail of the fuel injector of  FIG. 2 . In addition to the one-piece armature  400 , in a further feature of the present invention a guide  500  is employed, which allows an axial offset of the armature unit  352  relative to the valve seat  342  of the valve. The provision of the guide  500  can be combined with either a one-piece armature  400 , as shown in  FIG. 4 , or a two-piece armature unit  352  as shown in  FIG. 3 . 
       FIG. 5 , in an enlarged detail of  FIG. 2 , shows the armature  400  in combination with the guide  500 . Alternatively, instead of the one-piece armature  400 , a two-piece armature can be used, including the inner armature part  370  and the outer armature part  360  as shown in  FIG. 3 . 
     In a further variant of the present invention, shown in  FIG. 6  as a detail of  FIG. 2 , a guided armature  600  is used. For that purpose, part of the guided armature  600  is guided into a bore  610  in the magnet  110 ; the upper end of the guided armature  600  is designed cylindrically, so that the guided armature  600  is inserted by positive engagement and yet nevertheless movably into the bore  610  of the magnet  110 . In this way, with minimized radial play, an optimal perpendicular alignment of the guided armature  600  relative to the magnet  110  is attained. 
     In  FIG. 7 , a variant of the present invention is shown in which the one-piece armature  400  is aligned with the valve body  60  via at least one spacer sleeve  700 . 
     In  FIG. 8 , a variant of the invention can be seen in which a magnet in cartridge form  810  is used, which is connected by nonpositive or positive engagement to a magnet sleeve  800  and thus installed as a unit in the nozzle body  60 . 
     In the variant embodiments shown in  FIGS. 7 and 8  of the fuel injector proposed according to the invention, the valve seat  342  is shifted into the plane of the interface between the injector body  10  and the upper flat side of the valve body  30 . This has advantages for example in the assembly of the fuel injector. While in the embodiment shown in  FIG. 7  the electromagnet  110  is aligned with the valve body  30  via a spacer sleeve  700 , in the embodiment of  FIG. 8  the electromagnet  110  is built in, packaged as a “cartridge”, into the injector body  10 . In both versions in  FIGS. 7 and 8 , the magnet  110  can be joined by nonpositive and positive engagement to the spacer sleeve  700  surrounding it or the magnet sleeve  800  and thus installed as a preassembled unit in the assembly in the injector body  10  of the fuel injector, which facilitates the assembly. 
     The foregoing relates to the preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.