Patent Publication Number: US-2004041039-A1

Title: Common-ramp-injector

Description:
BACKGROUND OF THE INVENTION  
       [0001] The common rail injection system serves to inject fuel into direct-injection internal combustion engines. In this reservoir injection system, the generation of pressure and the injection are decoupled from one another in terms of both time and place. A separate high-pressure pump generates the injection pressure in a central high-pressure fuel reservoir. The onset of injection and the injection quantity are determined by the instant and duration of triggering of injectors that for instance are actuated electrically and that communicate with the high-pressure fuel reservoir via fuel lines.  
       PRIOR ART  
       [0002] German Patent Disclosure DE 196 50 865 A1 relates to a magnet valve for actuating a common rail injector. In FIG. 1 of this published, nonexamined patent disclosure, one such injector is shown. The injector communicates directly with a high-pressure fuel reservoir (common rail), which is constantly supplied with fuel that is at high pressure by a high-pressure feed pump. Via the magnet valve-controlled injector, the high-pressure fuel is delivered to the combustion chamber of the engine.  
       [0003] An injection by means of an injector in accordance with FIG. 1 of DE 196 50 865 A1 proceeds as follows: The opening and closure of the valve needle is controlled by the magnet valve. In the currentless state of the electrical magnet valve, an outlet throttle, by way of which the valve control chamber communicates with the fuel return, is closed by the valve member. Via an inlet throttle, the high pressure that is also present in the high-pressure fuel reservoir can then build up very rapidly in the valve control chamber. Together with a restoring spring, the pressure in the valve control chamber generates a closing force on the valve needle that is greater than the forces, resulting from the applied high pressure, that act on the other side on the valve needle in the opening direction. If the valve control chamber is opened toward the relief side by opening of the magnet valve, then the pressure in the small volume of the valve control chamber drops quite rapidly, since the valve control chamber is decoupled from the high-pressure side via the outlet throttle. As a consequence, the force acting on the valve needle in the opening direction and resulting from the high fuel pressure present at the valve needle predominates, so that the valve needle is moved upward and the injection openings are opened for injection. This indirect triggering of the valve needle via a hydraulic fuel booster system is employed because the forces required for fast opening of the valve needle cannot be generated directly by the magnet valve. The so-called control quantity needed then in addition to the injected fuel quantity reaches the fuel return via the throttle of the valve control chamber.  
       [0004] The injection quantity, in this common rail injection system used in the prior art, is determined by the triggering of the magnet valve, the adaptation of the inlet throttle to the outlet throttle, and the geometries of the valve piston and of the valve needle. The system becomes expensive because of the number of components required. Moreover, the injection quantity is subject to major variation because of the influence of the various parameters and tolerances.  
       SUMMARY OF THE INVENTION  
       [0005] The embodiment according to the invention has the advantage that fewer components are needed in the common rail injector, and so costs are reduced. Moreover, the number of influential parameters on the injection quantity is reduced, and the injection quantity is controlled more precisely. These advantages are attained according to the invention by an injector with high-pressure injection of fuel in self-igniting internal combustion engines, and the injector includes a hollow injector body, which on one end includes a valve seat and at least one injection opening. Furthermore, the injector of the invention includes a valve needle, which is disposed in an extension of a valve piston in the injector body, so that in the closed state it closes the at least one injection opening, and at least one spring, which keeps the injector closed in the pressureless state by pressing the valve needle into the valve seat. The injector further includes at least two magnet devices, which serve to open and close the injector directly.  
       [0006] The expense for at least two magnet devices for direct triggering is markedly less than for indirect triggering of the valve needle via a hydraulic fuel booster system with an outlet throttle and an inlet throttle. For the direct triggering of the valve needle, forces are required that cannot be brought to bear solely by a magnet device, for the given dimensions of the injector. The injector of the invention therefore includes at least two magnet devices, which together are capable of bringing adequately strong forces to bear to open the valve needle. 
     
    
    
     DRAWING  
     [0007] The present invention will be described in further detail below in conjunction with the drawing.  
     [0008] Shown are:  
     [0009]FIG. 1, a schematic illustration of an injector of the invention, with two magnet devices;  
     [0010]FIG. 2, a first embodiment of a valve needle tip of the invention;  
     [0011]FIG. 3, a graph showing the magnetic force as a function of the air gap between the electromagnet and the magnet armature;  
     [0012]FIG. 4, a second embodiment of a valve needle tip of the invention, with a throttle gap; and  
     [0013]FIG. 5, a third and fourth embodiment of a valve needle tip of the invention, also with a throttle gap. 
    
    
     EMBODIMENT VARIANTS  
     [0014]FIG. 1 shows an injector according to the invention, with two magnet devices  37 ,  38 . The injector comprises a hollow injector body  1 , which on one end has a valve seat  2  and a plurality of injection openings  3 . A valve needle  4  is disposed in an extension of a valve piston  5  in the injector body  1 . The valve needle  4  closes the injection openings  3  tightly, in the closed state of the injector, against the combustion chamber (not shown). In this state, accordingly no injection of fuel into the combustion chamber of the engine takes place.  
     [0015] The left half of the injector shown is a variant with two springs  6 ,  7 , while the right half shows a variant with one spring  8 . The springs  7  and  8  are compression springs, which keep the injector closed in the pressureless state. They can also serve to assure the closing operation of the opened injector at the end of an injection. The springs  6 ,  7 ,  8  are located in a spring chamber  9  contained in the injector body  1 . The inner spring  7  (when there are two springs) and the spring  8  (when there is one spring) rest on one end on a wall of the spring chamber  10 . On its other end, they strike a disk  11 , which is connected to the valve piston  5 . When the injector is open, the valve piston  5 , including the disk  11 , is displaced in the opening direction  12  into the spring chamber  9 , so that the spring  7 ,  8  becomes compressed and thus exerts a force in the closing direction  13  on the disk  11  and the valve piston  5 .  
     [0016] In the variant with two springs  6 ,  7 , the outer spring  6  likewise with one end strikes the wall of the spring chamber  10 , where it is secured. With its other end, the spring  6  is connected to an annular disk  14  that is braced on the injector body  1 . The outer spring  6  is prestressed to a defined force. The underside of the annular disk  14  is located at a spacing  15  from the top side of the disk  11 . If upon opening of the injector in the opening direction  12  the valve needle  4  along with the valve piston  5  and the disk  11  is moved by the spacing  15 , then the annular disk  14  rests on the disk  11 . Upon still farther opening of the injector than the spacing  15 , the disk  11  and the annular disk  14  are displaced jointly in the opening direction  12  in the spring chamber  9 , so that both springs  6 ,  7  are simultaneously compressed and exert the force on the valve piston  5  in the closing direction  13 .  
     [0017] In the preferred embodiment of the present invention, shown in FIG. 1, a high-pressure line  21  extends centrally in the longitudinal direction in the injector; it carries the fuel at high pressure, which is flowing into the injector from a high-pressure fuel reservoir (common rail) (not shown), through the injector to a fuel reserve chamber  22  of the injector. The fuel at high pressure passes through an inlet  23  into the high-pressure line  21 . The high-pressure line discharges into the spring chamber  9  (through the wall  10 ) and continues on the other side of the spring chamber  9  through the disk  11  and the valve piston  5 . In the region of the fuel reserve chamber  22 , the valve piston  5  has a plurality of openings  24 , through which the fuel reaches the fuel reserve chamber  22 . From there, the fuel can flow along the valve needle  4  to the injection opening  3 . A leak fuel line  27  serves to carry away leak fuel quantity.  
     [0018] In this preferred embodiment of the present invention, two magnet devices  37 ,  38  are used for directly opening and closing the injector; each has one magnet armature  16 ,  17  and one electromagnet  18 ,  19 . The electromagnets  18 ,  19  are solidly connected to the injector body  1 . The electromagnets  18 ,  19  are connected in parallel to a current source (not shown) via an electrical current terminal  25 .  
     [0019] In the preferred embodiment of the present invention, shown in FIG. 1, the magnet armatures  16 ,  17  have different strokes (h 1  and h 2 , respectively). The stroke (h 1 , h 2 ) is understood to mean the distance that the magnet armature  16 ,  17  travels in the opening direction upon opening of the injector until it contacts the associated electromagnet  18 ,  19 . FIG. 1 shows an injector of the invention in which the stroke h 1  of the first magnet armature  16  is shorter than the stroke h 2  of the second magnet armature  17 . Preferably, the stroke h 1  of the first magnet armature is from 30 to 60 μm in length, and the stroke h 2  of the second magnet armature is from 150 to 250 μm in length.  
     [0020] In this preferred embodiment of the present invention, the second magnet armature  17  is disposed fixedly on the valve piston  5 . Moreover, the first magnet armature  16  is disposed slidingly on the valve piston. With the injector closed, the first magnet armature  16  is located at an upper stop  20 , which is created by means of an annular bulge of the valve piston  8 . In this position of the first magnet armature  16 , it is connected by nonpositive engagement to the valve piston  5 , which has a diameter d 1 . With the injector closed, the first magnet armature  16  is kept at the upper stop  20  by a restoring spring  39 . When current is supplied to the electromagnets  18 ,  19 , the magnetic force of the first electromagnet  18  acts on the first magnet armature  16  in the opening direction  12 . At the same time, the magnetic force of the second electromagnet  19  acts on the second magnet armature  17  in the opening direction  12 . As a result of the magnetic force of the two electromagnets  18 ,  19 , the magnet armatures  16 ,  17  move the valve piston  5  along with the valve needle  4  in the opening direction  12 , since the second magnet armature  17  is connected solidly, and the first magnet armature  16  is connected via the upper stop  20 , to the valve piston  5 . Consequently, the valve needle  4  lifts from the valve seat  2 , and an injection of the fuel that is at high pressure takes place via the injection openings  3 .  
     [0021] The first magnet armature  16 , because of its shorter stroke h 1  during an opening event of the injector, is located on its associated first electromagnet  18  sooner than the second magnet armature  17 . However, since the first magnet armature  16  is disposed slidingly on the valve piston  5 , the second magnet armature  17 , including the valve piston  5  fixedly connected to it, can move onward in the opening direction  12 , until the second magnet armature  17  is also in contact with its associated second electromagnet  19 . The first magnet armature  16  slides over a portion  26  of the valve piston  5  that has a smaller diameter than the valve piston  5  at the upper stop  20 . Upon closure of the injector, the first magnet armature, with the aid of the restoring spring  39 , reaches its outset position at the upper stop  20  again.  
     [0022] Because of the two different strokes h 1 , h 2  of the magnet armatures  16 ,  17 , the possibility of stroke adaptation is advantageously afforded; that is, for small injection quantities, the short stroke h 1  of the first magnet armature  16  can be executed. Thus the motion of the valve needle  4 , which in the prior art has a ballistic course in the range under load, can be stably kept to a partial stroke (h 1 ). Consequently and advantageously, the variation in the injection quantity is reduced. The triggering of the partial stroke h 1  is possible via the current intensity and/or via how the spacing  15  is allocated. The partial stroke h 1  is set as precisely as is technically feasible, for instance by displacement of the electromagnet  18  with ensuing fixation by laser welding.  
     [0023] The injector shown in FIG. 1 is only one possible embodiment of the present invention. For instance, it is also conceivable for an injector of the invention to have two magnet devices  37 ,  38  which include two magnet armatures with equal-length strokes h that are mounted fixedly on the valve piston. When current is supplied to the two electromagnets, the valve needle is then moved by the stroke h in the opening direction by the magnetic force acting on the magnet armatures.  
     [0024] It is also for instance conceivable to supply current to the individual electromagnets via separate electrical terminals, making it possible to vary the magnetic force on the magnet armatures  16 ,  17  more freely.  
     [0025] In the embodiment of the present invention shown in FIG. 1, the diameter d 1  of the valve piston  5  (in the opening direction  12  relative to the upper stop  20 ) is equal to the diameter d 2  of the valve piston  5  (in the closing direction  13  relative to the second magnet armature  17 ). With the injector open, an equilibrium of forces prevails as a result of the high pressure in the opening direction and the closing direction ( 12 ,  13 ), since the effective surface areas on which the high pressure exerts a force in these two directions ( 12 ,  13 ) are the cross-sectional areas of the valve piston  5  having the diameters d 1  and d 2 . Thus in the open state of the injector, the force of the high pressure in the closing direction  13  is exerted on an area  
         A   1   open     =       π        (       d   1     2     )       2                   
 
     [0026] and in the opening direction  12  on a surface area  
         A   2   open     =         π        (       d   2     2     )       2     .                   
 
     [0027] If the diameters are equal, that is, if d 1 =d 2 , then (with the injector open), 
     A 1   open =A 2   open =A open , 
     [0028] and thus 
       F   1   open   =p·A   open   =F   2   open , 
     [0029] in which p stands for the high pressure. For closing the injector after the electromagnets  18 ,  19  have been shut off, an additional force is accordingly needed, which is exerted by the springs  6 ,  7 ,  8 .  
     [0030] In the closed state of the injector, the force from the high pressure on the valve piston  5  in the closing direction  13  is preferably greater than the force resulting from the high pressure in the opening direction  12 . In the embodiment of the present invention shown in FIG. 1, this is assured with the provision that d 1 =d 2 , since the effective surface area on which the high pressure exerts a force in the opening direction  12  on the valve needle  4  and the valve piston  5  is reduced, with the injector closed, by the valve seat face  28  (A S ). The force in the closing direction  13  F 1   closed  is accordingly greater than the force in the opening direction  12  F 2   closed . Then  
         A   1   closed     =       π        (       d   1     2     )       2           and           A   2   closed     =         π        (       d   2     2     )       2     -     A   S                     
 
     [0031] where if d 1 =d 2 , it follows that 
     
       A 
       2 
       closed 
       =A 
       1 
       closed 
       −A 
       S 
     
     [0032] and thus 
     A 2   closed &lt;A 1   closed , and F 2   closed &lt;F 1   closed . 
     [0033] The closed injector accordingly remains closed solely because of the high pressure. The requisite force for opening the injector is determined by the difference in surface area, A 1   closed −A 2   closed , and the requisite force for compressing the springs  7 ,  8 .  
     [0034] In a further embodiment (not shown) of the present invention, the diameter d 1 &lt;d 2 , but the difference in surface areas A 2   closed −A 1   open  is less than or at most equal to the valve seat area A S . In this embodiment of the present invention as well, because of the condition A 2   open −A 1   open ≦A S , it is assured that with the injector closed, the force F 1   closed  on the valve piston  5  and the valve needle  4  in the closing direction  13  is greater than or equal to the force F 2   closed  resulting from the high pressure in the opening direction  12 .  
     [0035] For closure of the open injector, in the variant where d 1 &lt;d 2 , compared to the variant where d 1 =d 2 , an additional force ΔF 
     
       ΔF=F 
       2 
       open 
       −F 
       1 
       open 
     
     [0036] must be brought to bear by the springs  6 ,  7 ,  8 , and this additional force is proportional to the difference in surface area 
       ΔA=A   2   open   −A   1   open . 
     [0037]FIG. 2 shows an embodiment according to the invention of a valve needle. This is a valve needle  4  that has a form corresponding to the prior art but has a lesser diameter d in the region which, when the injector is closed, rests in the valve seat region  31  on the injector body  1 . The lesser diameter d is required so that the injector can be opened with the maximum possible magnetic forces by the electromagnets  18 ,  19 . In the present invention, the diameter d can for instance amount to 1.1 mm.  
     [0038]FIG. 3 shows a graph of the magnetic force as a function of the air gap between the electromagnet and the magnet armature. The magnetic force F is less, the larger the air gap h between the electromagnet  18 ,  19  and the magnet armature  16 ,  17 . With the injector closed, the valve needle tip rests on the valve seat region  31 , and the air gap between the second electromagnet  19  and the second magnet armature  17  assumes its maximum size (for instance, 0.25 mm). At this air gap size 1, the second magnet armature  17  is attracted by the second electromagnet  19  with the magnetic force B. At the partial stroke h 1 , the air gap size is smaller (air gap size 2), and the second magnet armature  17  is attracted by the greater magnetic field force A. The magnetic force between the first magnet armature  17  and the first electromagnet  19  behaves in the same way.  
     [0039]FIG. 4 shows an embodiment of the valve needle that is preferred according to the invention. To reduce the spring force required to close the open injector, particularly for the variant where d 1 &lt;d 2 , the valve needle  4  and the valve needle tip  29  are shaped such that there is a throttle gap  30  between the valve needle  4  and the injector body  1 . During the injection event, the pressure in the valve seat region  31  is reduced by means of the throttle gap  30 , thus reinforcing the closing operation.  
     [0040]FIG. 5 shows two further preferred embodiments of a valve needle of the invention, one in the left half and the other in the right half of the drawing. In both embodiments shown, the valve needle  4  is again shaped such that with the injector open, between the valve needle  4  and the injector body  1  there is a throttle gap  30 , which reduces the pressure in the valve seat region  31 . In this embodiment, the throttling is reinforced still further compared to the embodiment shown in FIG. 4, since the throttle gap  30  extends not only within the conical valve seat region  31  but also along part of the cylindrical bore  33  in the valve body  1 . In the embodiment shown in the right half of FIG. 5, this throttle gap  30  occurs along a portion of the cylindrical bore  33  of the valve body  1  through a partial region  32  of the valve needle  4  in which the valve needle  4  has a larger diameter. As a result, the interstice between the valve needle  4  and the valve body  1  is reduced in size, so that along this partial region  32 , once again there is a throttle gap  30 . This throttle gap  30  continues to exist along the partial region  32  regardless of the stroke of the valve needle  4 .  
     [0041] Unlike the above, in the preferred embodiment of the injector of the invention shown in the left half of FIG. 5, the existence and length of the throttle gap along the partial region  34  is dependent on the position of the valve needle  4 . The farther the valve needle  4  is displaced in the opening direction  12  relative to the valve body  1 , the shorter is the overlap  35  between a region  36  of the bore  33  of smaller diameter and the partial region  34  of the valve needle  4  of larger diameter. Beyond a stroke of the valve needle  4  that is dependent on the width and disposition of the regions  34  and  36 , there is no longer any overlap  35 , and the spacing between the valve body  1  and the valve needle  1  becomes greater, so that throttling no longer occurs.  
     [0042] This preferred embodiment of the injector of the invention shown in the left half of FIG. 5 can advantageously be combined with the embodiment that has two springs. Upon opening of the injector, only the longer spring counteracts the magnetic forces. Beyond a certain prestroke of the longer spring (corresponding to spacing  15  in FIG. 1), both springs counteract the opening of the injector. However, the spring forces can be overcome, since even when the injector is partly open the high pressure acts in the seat region upon the valve needle  4 , and the magnetic forces have already increased because of the slight spacing between the respective magnet armature  16 ,  17  and its electromagnet  18 ,  19 . The injector opens completely, and the fuel injection takes place. For closure, the electromagnets are switched off. At first, both springs  6 ,  7  act on the valve piston  5 . When the shorter spring  6  with the annular disk  14  reaches its stop in the injector body  1 , and the longer spring is acting alone in the closing direction on the valve piston, the overlap  35  already becomes operative, and the hydraulic forces (pressure drop in the valve seat region  31 ) reinforce the complete closure of the injector.