Abstract:
A fuel injection apparatus having a fuel injector fed by a high-pressure fuel source and having an injection valve with injection nozzles associated with coaxial inner and outer nozzle needles can be actuated in a pressure-dependent manner to open and close various injection cross sections at the injection nozzles. A pressure surface of the outer nozzle needle is associated with a closing chamber. To actuate the outer nozzle needle, a first on/off valve can connect the closing chamber to a low-pressure/return system. The inner nozzle needle has a control piston whose pressure surface protrudes into a second control chamber, and a second on/off valve is can connect the control chamber to the low-pressure/return system so that when the second on/off valve is actuated, the pressure is relieved in the second control chamber. This permits a separate actuation of the outer nozzle needle and inner nozzle needle.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to an improved fuel injection apparatus for internal combustion engines.  
         [0003]     2. Description of the Prior Art  
         [0004]     A fuel injector, which has two rows of injection nozzle holes that are associated with an inner nozzle needle and an outer nozzle needle that is positioned coaxial to the inner one, is known, for example, from DE 102 05 970 A1. Injection nozzles of this kind, which can be actuated in a pressure-dependent manner to open various injection cross sections, are also referred to as vario-nozzles. The outer and inner nozzle needles are each associated with a control piston that acts on a respective fuel-filled hydraulic chamber so that the hydraulic chambers function as actively operating control chambers. The two control chambers are hydraulically connected to each other via a connecting conduit. The control chamber of the outer nozzle needle can be connected to a low-pressure return system via an outlet throttle. The connecting conduit is dimensioned so that when the outlet throttle opens, the pressure first drops in the control chamber of the outer nozzle needle and then, only after a delay, does the pressure drop in the control chamber of the inner nozzle needle.  
         [0005]     In order to increase the injection pressure, which is greater than the pressure level prevailing in the pressure accumulator (common rail), DE 102 29 417 A1 has disclosed a fuel injection apparatus that has a pressure boosting unit and, to further improve injection characteristics and increase efficiency, is also equipped with a vario-nozzle that has an inner and an outer nozzle needle. Spring assistance sets the opening pressure of the inner nozzle needle to a constant level and, with the aid of an additional assisting pressure, sets a particular ratio of rail pressure to opening pressure. This makes it possible to adapt the hydraulic flow through the fuel injector to the load point of the internal combustion engine. The inner nozzle needle is set so that it only opens at relatively high pressures of for example greater than 1500 bar in order to thus achieve favorable emissions levels in the partial load range of the engine. The setting of the constant opening pressure for the inner nozzle needle here is very tolerance-sensitive since the opening of the inner nozzle needle is accompanied by a jump in the injection quantity. In this connection, manufacturing tolerances can result in a particularly unpleasant feel. In the other variants for achieving the opening pressure of the inner nozzle needle by means of the constant ratio between the assistance pressure and the nozzle pressure, the inner nozzle needle also opens in the partial load range of the engine.  
         [0006]     In order to prevent the tolerances in the duration of the control valve actuation from affecting the injection quantity in fuel injection apparatuses equipped with pressure boosters, the prior DE patent application 102 29 415.1 has already proposed damping the opening speed of an individual nozzle needle without impairing a rapid closing of the nozzle needle. A damping piston is axially guided in the closing chamber of the nozzle needle, delimits a damping chamber, and communicates with the closing chamber of the nozzle needle via an overflow conduit.  
       OBJECT AND SUMMARY OF THE INVENTION  
       [0007]     The object of the present invention is to further improve the adaptability of the fuel injection apparatus to the operating points of the internal combustion engine and to meet the demand for a homogeneous combustion process.  
         [0008]     The fuel injection apparatus according to the present invention has the advantage of permitting an improved adaptation of the duration and volume of the injection to the operating point of the internal combustion engine. A first on/off valve is provided to actuate the outer nozzle needle and a second on/off valve is provided to actuate the inner nozzle needle. The first on/off valve can connect a closing chamber for the outer nozzle needle to a low-pressure/return system. In order to actuate the inner nozzle needle, the second on/off valve can connect a control chamber associated with the first nozzle needle to the low-pressure/return system so as to relieve the pressure in the control chamber. This permits a separate actuation of the outer and inner nozzle needles so that the two nozzle needles of the vario-nozzle can be activated independently of each other. As a result, the quantity or volume injected by means of the two rows of injection nozzle holes can be varied in that from one injection to the next, it is possible to freely select from among an injection via the first row of holes, the second row of holes, or both rows of holes together. It is also possible to freely select between the injection pressure level with pressure boosting and without it.  
         [0009]     The entry direction of the injection jet into the combustion chamber, which is produced by the inclination of the nozzle bore and is also referred to as the vertical angle, influences not only the pressure and the injection angle, but also the combustion process of the engine. If the two rows of holes of the nozzle bores for the injection nozzles are provided with different inclinations and/or spray cones, then there is the potential, by means of the separately actuatable rows of holes, of working with different vertical angles so that with a very small vertical angle, a homogeneous combustion with an early injection onset can be achieved without wetting the cylinder wall of the engine. Since homogeneous combustion processes can only be used for certain engine loads, the flexible injection with different vertical angles or spray angles also offers the possibility of an optimal adaptation to different combustion concepts.  
         [0010]     Advantageous improvements and updates of the invention are disclosed. The filling of the control chamber from the rail pressure system can be suitably provided via a throttle or a check valve; the check valve prevents the control chamber from emptying into the control line.  
         [0011]     The fact that the two nozzle needles can be actuated independently of each other permits this actuation concept to be used in a particularly suitable fashion in so-called leakless injector nozzles in which a separate fuel supply is provided for the inner injection nozzles. The separate fuel supply leads from a nozzle chamber associated with the outer nozzle needle to a pressure shoulder on the inner nozzle needle upstream of the inner injection nozzle. The separate fuel supply line is thus suitably embodied as an intermediate chamber between the inner nozzle needle and the outer nozzle needle. A rapid closing of the outer nozzle needle is achieved if a dividing line is provided between the end surface of the outer nozzle needle and an associated damping piston inside a closing chamber and in addition, there is a hydraulic connection between the damping chamber and the closing chamber.  
         [0012]     In a particularly suitable embodiment, it is also possible to combine the independent actuation of the two nozzle needles of the vario-nozzle with a pressure boosting unit that is integrated into the fuel injector. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments, taken in conjunction with the drawings, in which:  
         [0014]      FIG. 1  shows a schematic representation of a first exemplary embodiment of a fuel injection apparatus according to the present invention,  
         [0015]      FIG. 2  shows a schematic representation of a second exemplary embodiment of a fuel injection apparatus according to the present invention,  
         [0016]      FIG. 3  shows a schematic representation of a third exemplary embodiment of a fuel injection apparatus according to the present invention, and  
         [0017]      FIG. 4  shows a schematic representation of a fourth exemplary embodiment of a fuel injection apparatus according to the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     The fuel injection apparatuses shown in  FIGS. 1 through 4  include a fuel injector  1  and a high-pressure accumulator  2  (common rail); the high-pressure accumulator  2  supplies highly pressurized fuel to the fuel injector  1 . The fuel injector  1  includes a pressure booster  5 , a servo-valve  6 , and an injection valve  9  whose combustion chamber end injects fuel into a combustion chamber, not shown, of an internal combustion engine. The servo-valve  6 , which is embodied for example in the form of a 3/2-way valve, has a first on/off valve  7  and a control valve  8  actuated by it. In the present exemplary embodiment, an electromagnet actuates the on/off valve  7 . However, a piezoelectric actuator can also take the place of the electromagnet. In other embodiment forms for the servo-valve  6 , it is also possible to use a directly-controlled solenoid valve or a pressure-balanced 3/2-way valve with a piezoelectric actuator.  
         [0019]     The injection valve  9  has a vario-nozzle with an outer nozzle needle  11  and an inner nozzle needle  12 . The nozzle needles  11 ,  12  are guided coaxially one inside the other and can move longitudinally independently of each other. The vario-nozzle has two rows of injection nozzle holes, with outer injection nozzles  13  and inner injection nozzles  14 ; the outer nozzle needle  11  is associated with the outer injection nozzles  13  and the inner nozzle needle  12  is associated with the inner injection nozzles  14 . The outer nozzle needle  11  has a pressure shoulder  16  inside a pressure chamber  15 . At the combustion chamber end, the inner nozzle needle  12  is provided with an additional pressure shoulder  18  upstream of the inner injection nozzles  14 . At the end oriented away from the combustion chamber, the outer nozzle needle  11  is associated with a closing chamber  20  in which the outer nozzle needle  11  has a pressure surface  21  that is oriented toward the closing chamber and acts in the closing direction. The outer nozzle needle  11  is also associated with a damping piston  41  that is guided in a bore  42  adjoining the closing chamber  20 .  
         [0020]     A closing spring  44  in the closing chamber  20  prestresses the damping piston  41 , which, inside the closing chamber  20 , has an end surface  47  that is oriented toward the nozzle needle and rests against the pressure surface  21  of the outer nozzle needle  11  oriented toward the closing chamber. There is a dividing line  45  between the end surface  47  of the damping piston  41  oriented toward the nozzle needle and the pressure surface  21  of the outer nozzle needle  11 . Inside a damping chamber  50 , the damping piston  41  also has a pressure surface  49  embodied in the form of an annular end surface.  
         [0021]     The inner nozzle needle  12  is connected to a control piston  43 , which is embodied in the form of a piston rod and extends through the damping piston  41 . In the exemplary embodiments according to  FIGS. 1 through 3 , a flow conduit  46  in the form of an annular gap that extends from the damping chamber  50  to the dividing line  45  is provided between the control piston  43  and the inner cylindrical wall of the damping piston  41 . The control piston  43  for the inner nozzle needle  12 , which piston is embodied in the form of a piston rod, extends through the damping chamber  50  and protrudes into a control chamber  53  with a pressure surface  52  at the end oriented toward the control chamber. At the transition to the control piston  43 , the inner nozzle needle  12  also has a step  22  that is oriented in the closing direction of the inner nozzle needle  12  and functions as a pressure shoulder that assists the closing process of the inner nozzle needle.  
         [0022]     From the schematically depicted high-pressure accumulator  2 , fuel travels via a combined check valve/throttle valve  23  and a rail pressure line  24  into a pressure chamber  25  of the pressure booster  5 . In addition to the above-mentioned pressure chamber  25 , the pressure booster  5  has a differential pressure chamber  26  and a high-pressure chamber  27 . The pressure booster  5  contains an axially movable stepped piston  30  that includes a first partial piston  31 , which, in comparison to a second partial piston  32 , has a larger, guidance-enabling diameter. The stepped piston  30  can be embodied either as two separate components or as a single component. In addition, the stepped piston  30  has a piston rod  33 , which protrudes into the pressure chamber  25  and is provided with a spring retainer  34  for a closing spring  35 . The end surface of the second partial piston  32  of the stepped piston  30  delimits the high-pressure chamber  27  to which a high-pressure line  36  is connected, which acts on the nozzle chamber  15  of the injection valve  9  with very highly pressurized fuel. The differential pressure chamber  26  of the pressure booster  5  has a first control line  28  and a second control line  29  branching from it; the first control line  28  is connected to the control valve  8  and, via a closing chamber throttle  54 , the second control line is connected to the closing chamber  20  of the injection valve  9 . The closing chamber  20  is also connected to the high-pressure line  36  via a check valve  55 . The control chamber  50  is connected to the second line  29  via an outlet throttle  56 . Another line  57  containing an additional throttle  58  leads from the pressure chamber  25  to the control chamber  53 .  
         [0023]     The control valve  8  is provided with a control piston  81 , which has a pressure surface that delimits a control chamber  82  at its end oriented toward the control valve. A connecting conduit  83  is incorporated into the control piston  81  and connects the pressure chamber  25  to the control chamber  82  via a throttle  84 . A sealing seat  78  and a control edge  85  are provided on the control piston  81 . The sealing seat  78  disconnects a valve chamber  89  from a low-pressure chamber  86  that is connected to a return line  87 . The return line  87  is connected to a low-pressure/return system  88 . The control edge  86  disconnects the pressure chamber  25  from the valve chamber  89  into which the line  28  feeds.  
         [0024]     The on/off valve  7  has an actuator control chamber  73  and an actuator low-pressure chamber  75 ; the control chamber  73  is connected to the control valve control chamber  82  via a control line  76  and the low-pressure chamber  75  is connected to the low-pressure/return system  88  via an additional return line  77 .  
         [0025]     The fuel injector  1  also has a second on/off valve  90  that has a control piston  91  that divides an actuator pressure chamber  92  from a low-pressure chamber  93 . A control line  94  leads from the pressure chamber  92  to the control chamber  53 . The low-pressure chamber  93  is connected to an additional return line  95  that also leads to the low-pressure/return system  88 .  
         [0026]     It is also conceivable for the second on/off valve  90  to be positioned at the top end of the fuel injector  1 . For the sake of simplicity, it is also possible for it to be located outside the fuel injector  1 . In this instance, the on/off valve  90  can function centrally for all of the cylinders of an internal combustion engine. In this scenario the option to use it is contingent on the number of cylinders and on the injections required since after each activation of the inner nozzle needle  12 , an injection pause must occur in all cylinders in order to prevent an uncontrolled opening of the inner injection nozzles  14 . An embodiment form of this kind has significant space advantages in the fuel injector  1 . However, it is necessary to provide an additional hydraulic connection for the fuel injector  1 . An external on/off valve  90  must also have sufficient dynamics to achieve an activation during an injection pause. The operating pressure can conceivably be the rail pressure or a defined low pressure of for example 5 to 50 bar. This consequently requires a corresponding design of the pressure surface  52  in the control chamber  53 . When pressures on the order of roughly 5 bar are used, the second on/off valve  90  can be embodied in the form of a low-pressure on/off valve. In all variants, the injection nozzles  13 ,  14  and the damping chamber  50  are subjected to pressure. Prevention of leakage via the guide surfaces between the inner and the outer nozzle needles  11 ,  12  requires selection from among the intrinsically known measures, e.g. a double needle seat on the outer nozzle needle  11  or an additional leakage drain between the nozzle needles  11 ,  12 .  
         [0027]     In a normal state in which the injection nozzles  13 ,  14  are closed by the outer and inner nozzle needles  11 ,  12 , all of the pressure chambers in the pressure booster  5  are subjected to rail or system pressure. The stepped piston  30  is thus pressure balanced. In this state, the pressure booster  5  is deactivated; the return spring  35  has returned the stepped piston  30  to its starting position and the pressure chamber  25  has been filled via the check valve  23 . In the normal state, rail or system pressure prevails in the closing chamber  20 , the damping chamber  50 , and the control chamber  53 . Because of the area ratios of the end surfaces  49 ,  52  and the pressure shoulders  16 ,  18  embodied on the nozzle needles  11 ,  12 , a hydraulic closing pressure acts on the inner and outer nozzle needles  11 ,  12 . The compression spring  44  acting on the damping piston  41  and therefore on the outer nozzle needle  11  also assists the closing process. As a result, the rail pressure can be present in the nozzle chamber  15  on a constant basis without causing the outer nozzle needle  11  to open.  
         [0028]     In order to cause the outer nozzle needle  11  to open, the pressure in the nozzle chamber  15  must rise above the rail pressure, which is achieved by switching on the pressure booster  5 . This is initiated, as shown in  FIGS. 1 through 4 , by a depressurization of the differential pressure chamber  26  through activation of the electromagnet of the on/off valve  7 , which causes a depressurization of the control valve control chamber  82  into the low-pressure/return system via the actuator control chamber  73  and the actuator low-pressure chamber  75 . This causes the control piston  81  of the control valve  8  to lift, as a result of which the control edge  85  closes the connection to the pressure chamber  25 . At the same time, a connection is opened up between the valve chamber  89  and the low-pressure chamber  86 , as shown in  FIGS. 1 through 4 . As a result, the differential pressure chamber  26  is connected to the low-pressure/return system  88  via the line  28 . The pressure in the differential pressure chamber  26  decreases, as a result of which the pressure booster  5  is activated and the partial piston  32  of the stepped piston  30  compresses the fuel in the high-pressure chamber  27 . The compressed fuel travels via the high-pressure line  36  into the nozzle chamber  15 . At the same time, the pressure in the closing chamber  20  is relieved via the closing chamber throttle  54  so that the action of the high-pressure on the pressure shoulder  16  causes the outer nozzle needle  11  to lift up, as shown, as a result of which the injection via the outer injection nozzles  13  begins. Due to the resulting upward movement of the outer nozzle needle  11 , the end surface  49  of the damping piston  51  compresses a volume in the damping chamber  50 ; the compressed fuel can flow out of the damping chamber  50  via the outlet throttle  56  into the unpressurized line  29 . The outlet throttle  56  has a more powerful throttle action than the closing chamber throttle  54  so that the damping piston  41  can execute a damping action in the damping chamber  50 . The opening speed of the outer nozzle needle  11  and therefore the injection rate can be determined through a suitable dimensioning of the outlet throttle  56  and the closing chamber throttle  54 .  
         [0029]     The motor control unit, not shown, then actuates the additional on/off valve  90  and the control chamber  53  is connected to the low-pressure/return system  88  via the actuator pressure chamber  92  and the low-pressure chamber  93 . Due to the throttle  58  provided in the line  57  in the exemplary embodiment according to  FIG. 1 , less replenishing fuel flows out of the pressure chamber  25  so that the pressure is relieved in the control chamber  53  and as a result, the inner nozzle needle  12  lifts away from the inner injection nozzles  14 . The separate actuation of the first on/off valve  7  and the second on/off valve  90  also makes it possible, by implementing a corresponding actuation, to open only the outer nozzle needle  11 , to open the outer nozzle needle  11  and the inner nozzle needle  12  in sequence, or to open both nozzle needles  11 ,  12  simultaneously, in order to thus achieve different injection rates. This permits a flexible injection at various pressures and injection angles and consequently makes it possible to implement an optimum adaptation to various combustion concepts in the engine.  
         [0030]     In the exemplary embodiments shown in the remaining figures, components that are the same are provided with the same reference numerals. In the exemplary embodiment shown in  FIG. 2 , the control chamber  53  for the inner nozzle needle  12  is not connected to the pressure chamber  25  of the pressure booster  5 , but is instead connected to the control line  29  via a check valve  97 . The check valve  97  functions in opposition to the emptying direction leading from the control chamber  53  so that the check valve  97  only permits a filling of the control chamber  53  from the control line  29 . An actuation of the second on/off valve  90  causes the inner nozzle needle  12  to open, as has been described in conjunction with  FIG. 1 .  
         [0031]     In the exemplary embodiment in  FIG. 3 , a fuel injector  1  has an injection valve  10  equipped with a vario-nozzle in which the inner injection nozzles  14  are supplied with fuel via a separate fuel supply  101 . For example, the separate fuel supply is embodied in the form of an intermediate chamber or an annular gap between the inner nozzle needle  12  and the outer nozzle needle  11 . In addition, a connecting conduit  102  is routed, for example radially, through the outer nozzle needle  11  and connects the nozzle chamber  15  to the fuel supply  101  so that the injection pressure prevailing in the nozzle chamber  15  also prevails against the pressure shoulder  18  of the inner nozzle needle  12  at the combustion chamber end. This embodiment produces an intrinsically known leakless vario-nozzle in which the outer nozzle needle  11  is provided with a double seat, not shown, that functions as a sealing seat at the combustion chamber end. As in the exemplary embodiments 1 and 2, the activation of the outer nozzle needle  11  is initiated by means of the first on/off valve  7  with the interposition of the pressure boosting unit  5 . Here, too, the opening of the outer nozzle needle  11  is damped by means of the damping piston  41 . In the exemplary embodiment in  FIG. 3 , the control chamber  53  is connected to the high-pressure line  36  via a hydraulic connection  104  that contains a throttle  105 . A connection via the check valve  55  to the closing chamber  20  is also provided for the filling of the control chamber  52 . As a result, in the depressurized state, the control chamber  53  is coupled to the rail pressure via the closing chamber  20 . Through additional actuation of the second on/off valve  90 , the row of holes of the inner injection nozzles  14  can be opened and closed at any time. In this exemplary embodiment, the separate fuel supply for the inner injection nozzles  14  makes it possible to use a separate actuation of the inner nozzle needle  12  to execute a stroke-controlled injection at rail pressure without the interposition of the pressure boosting unit  5 . This permits short injection intervals and an advantageous multiple injection due to low pressure fluctuations. In combination with a slight inclination of the bores for the injection nozzles  14 , it is possible to achieve an early injection with a homogeneous combustion.  
         [0032]     The exemplary embodiment according to  FIG. 4  uses an injection valve  100  likewise equipped with a leakless vario-nozzle. As in the exemplary embodiment according to  FIG. 3 , the inner injection nozzles  14  are provided with a separate fuel supply  101  between the inner and outer nozzle needles  11 ,  12  and via the connecting conduit  102 . In this exemplary embodiment, though, the control chamber  53  is not connected to the high-pressure line  36 , but—as in the exemplary embodiments according to  FIGS. 1 and 2 —is connected via the line  57  and the throttle  58  to the pressure chamber  25  of the pressure boosting unit  5 . As a result, the control chamber  53  is coupled to the rail pressure prevailing in the pressure chamber  25 . Also in contrast with the exemplary embodiment of the leakless vario-nozzle in  FIG. 3 , there is no hydraulic connection between the damping chamber  50  and the closing chamber  20 . In this exemplary embodiment, the closing of the outer nozzle needle  11  is achieved merely by means of the pressure surface  21 , assisted by the compression spring  44 . Here, too, the inner nozzle needle  12  is actuated by means of the second on/off valve  90 . With an adapted pressure surface  52 , this embodiment form permits the use of an injection valve with low requirements regarding its capacity to resist high-pressure leaks and withstand high-pressure strains.  
         [0033]     It is also conceivable to use the actuation of the vario-nozzles  10 ,  100  described in  FIGS. 1 through 4  without a pressure booster  5 .  
         [0034]     The foregoing relates to 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.