Abstract:
A fuel injection is effected by means of a high-pressure pump ( 2 ) and a pressure reservoir chamber ( 6 ) for generating and storing a first system pressure. This system pressure is not used for injection; instead, by means of the pressure booster unit ( 9 ), a higher injection pressure is generated during the injection, and this injection pressure can be reduced to shape the course of injection. By means of this invention, an improved capability of metering the fuel injection and an improved execution of fast switching times are achieved.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 00102576 filed on Aug. 2, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an improved method of and an apparatus for performing a fuel injection into an internal combustion engine. 
     2. Description of the Prior Art 
     For better comprehension of the description and the claims, several terms will be defined below: The fuel injection according to the invention can be performed under stroke control or pressure control. Within the scope of the invention, the term stroke-controlled fuel injection is understood to mean that the opening and closing of the injection opening is effected with the aid of a displaceable valve member on the basis of the hydraulic cooperation of the fuel pressures in a nozzle chamber and in a control chamber. A pressure reduction inside the control chamber causes a stroke of the valve member. Alternatively, the deflection of the valve member can be effected by a final control element (actuator). In a pressure-controlled fuel injection according to the invention, by means of the fuel pressure prevailing in the nozzle chamber of an injector the valve member is moved counter to the action of a closing force (spring), so that the injection opening is uncovered for an injection of the fuel out of the nozzle chamber into the cylinder. The pressure at which fuel emerges from the nozzle chamber into a cylinder of an internal combustion engine is called the injection pressure, while the term system pressure is understood to mean the pressure at which fuel is available or stored inside the fuel injection system. Fuel metering means furnishing a defined fuel quantity for injection. Leakage is understood to mean a quantity of fuel that occurs in operation of the fuel injection system (such as a guide leakage), is not used for injection, and is pumped back to the fuel tank. The pressure level of this leakage can have a standing pressure, and subsequently the fuel is pressure-relieved to the pressure level of the fuel tank. 
     A stroke-controlled injection has already been disclosed by German Patent Disclosure DE 196 19 523 A1. The attainable injection pressure is limited here by the pressure reservoir chamber (rail) and the high-pressure pump to approximately 1600 to 1800 bar. 
     To elevate the injection pressure, a pressure booster unit is possible, of the kind known for instance from U.S. Pat. No. 5,143,291 or U.S. Pat. No. 5,522,545. The disadvantage of these known pressure-boosted systems resides in a lack of flexibility of injection and poor quantity tolerance in the metering of small fuel quantities. 
     In a fuel injection system described in Japanese Patent Disclosure JP 08277762 A, two pressure reservoir chambers with different pressures are provided for the sake of increasing the flexibility of injection and the metering accuracy of the pre-injection. These two pressure reservoir chambers require major engineering effort and high production costs, and yet the maximum injection pressure is still limited by the fuel pump and the pressure reservoir chamber. 
     SUMMARY OF THE INVENTION 
     For better metering capability of the injection and execution of fast switching times, according to the invention, an improved method of and apparatus for pre-injection and post-injection at a lesser injection pressure than the main injection can be performed replicably. A high Injection pressure at a low pressure in the central pressure reservoir chamber can be achieved. The high-pressure generation in the fuel takes place directly in the region of the injection (metering), so that the efficiency is increased as a consequence of a smaller high-pressure volume. The use of motor oil to trigger the pressure booster unit in one embodiment assures increased safety and reliability in the performance of the method. In another embodiment, the injection pressure can be generated hydraulically, while the portion generated mechanically by means of a high-pressure pump is stored in the pressure reservoir chamber and is not used for the injection. Because of the low pressure, the load on the high-pressure pump is reduced, since this pump is not used to fill the pressure reservoir chamber, but only for the injection per se. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages will be apparent from the description contained below, taken with the drawings, in which: 
     FIG. 1 is a schematic view of a first stroke-controlled fuel injection system; 
     FIG. 2 schematically illustrates a second stroke-controlled fuel injection system 
     FIG. 3 illustrates a third stroke-controlled fuel injection system, using a separate pressure fluid; 
     FIG. 4 illustrates a fourth stroke-controlled fuel injection system, using a pressure limitation in the pressure booster unit; 
     FIG. 5 illustrates a first pressure-controlled fuel injection system; 
     FIG. 6 illustrates a second pressure-controlled fuel injection system; 
     FIG. 7 illustrates a third pressure-controlled fuel injection system, using a separate pressure fluid; 
     FIG. 8 illustrates a fourth pressure-controlled fuel injection system, using a pressure limitation in the pressure booster unit; and 
     FIG. 9, a fifth pressure-controlled fuel injection system with a variable injection nozzle. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the first exemplary embodiment, shown in FIG. 1, of a fuel injection system  1 , a quantity controlled fuel pump  2  pumps fuel  3  out of a tank  4  via a feed line  5  into a central pressure reservoir chamber  6  (common rail). From the pressure reservoir chamber  6 , a plurality of pressure lines  7  corresponding in number to the number of individual cylinders of an internal combustion engine to be supplied lead away to the individual injectors  8 . Inside each of the injectors  8  (injection devices) protruding into the combustion chamber of the engine—in FIG. 1, only one of the injectors  8  is shown—, there is a pressure booster unit  9 . The pressure line  11  can be connected with the aid of a valve unit  10  for triggering the pressure boosting (3/2-way valve) to the pressure line  7 , or can be made to communicate with a leakage line  12  A system pressure of approximately 200 bar to 1000 bar, which is further boosted by the pressure booster unit  9 , can be stored in the pressure reservoir chamber  6 . 
     The pressure means  17  can be subjected to pressure at one end with the aid of the valve unit  10  and the pressure line  7 . A differential chamber  171  is pressure-relieved by means of the leakage line  15 , so that the pressure means  17  can be displaced to reduce the volume of a pressure chamber  13 . The pressure means  17  is moved in the compression direction, so that fuel compressed in the pressure chamber  13  (first injection pressure) can be delivered to a control chamber  19  and a nozzle chamber  20 . A check valve  14  prevents the return flow of compressed fuel into the pressure reservoir chamber  6 . By means of a suitable ratio of the areas in a primary chamber  13 ′ and the pressure chamber  13 , a second, higher pressure can be generated in this way. If the primary chamber  13 ′, with the aid of the valve unit  10 , is connected to the leakage line  12 , then the restoration of the pressure means  17  and the refilling of the pressure chamber  13  take place. Because of the pressure ratios in the pressure chamber  13  and the primary chamber  13 ′, the check valve  14  opens, so that the pressure chamber  13  is at rail pressure (pressure of the pressure reservoir chamber  6 ), and the pressure means  17  hydraulically one or more springs can be disposed in the chambers  13 ,  13 ′ and  17 ′. 
     By throttling inside one of the valves  10  or  29 , an injection pressure that is variable during the injection and thus a shaping of the course of injection can be achieved by means of a cross-sectional control; the pressure in the control chamber  19  is varied when the cross section of the valve  29  is controlled, and thus throttling of the injection pressure is attained at the valve sealing face  22  via the valve member  21 . To achieve a continuous cross-sectional control, both piezoelectric actuators and high-speed magnet actuators are conceivable. By providing multi-stage valves, instead of a continuous shaping of the injection pressure, a plurality of different injection pressure levels during injection can be created by means of different throttle positions. 
     In pressure line  18  communicating with the pressure chamber  13 , a pressure builds up that also prevails in the control chamber  19  and the nozzle chamber  20 . The injection takes place via fuel metering with the aid of a pistonlike valve member  21  that is axially displaceable in a guide bore and that has a conical valve sealing face  22  on one end, with which it cooperates with a valve seat face on the injector housing of the injector unit  8 . Injection openings are provided at the valve seat face of the injector housing. 
     Inside the nozzle chamber  20 , a pressure face pointing in the opening direction of the valve member  21  is exposed to the pressure prevailing there, which is delivered to the nozzle chamber  20  via the pressure line  18 . Coaxially to a valve spring  23 , a pressure piece  24  also engages the valve member  21  and with its face end  25  remote from the valve sealing face  22 , the pressure piece defines the control chamber  19 . From the fuel pressure connection stub, the control chamber  19  has an inlet with a first throttle  26  and an outlet to a pressure relief line  27  with a second throttle  28 , which is controlled by a 2/2-way valve  29 . 
     The nozzle chamber  20  continues across an annular gap between the valve member  21  and the guide bore, up to the valve seat face of the injector housing. By way of the pressure in the control chamber  19 , the pressure piece  24  is subjected to pressure in the closing direction. 
     Upon actuation (opening) of the 2/2-way valve  29 , the pressure in the control chamber  19  can be reduced, so that a consequence the pressure force in the nozzle chamber  20 , exerted in the opening direction on the valve member  21 , exceeds the pressure force exerted on the valve member  20  in the closing direction. The valve sealing face  22  lifts from the valve seat face, and fuel is injected. The pressure relief of the control chamber  19  and thus the stroke control of the valve member  21  can be varied by way of the dimensioning of the throttle  26  and the throttle  28 . 
     The end of injection is initiated by re-actuation (closure) of the 2/2-way valve  29 , which decouples the control chamber  19  from the pressure relief line  27  again, so that once again a pressure that can move the pressure piece  24  in the closing direction builds up in the control chamber  19 . 
     The valve units are actuated for opening or closing or switching over by electromagnets. The electromagnets are triggered by a control unit, which is capable of monitoring and processing various operating parameters (engine rpm, etc.) of the engine to be supplied. 
     In place of the magnet-controlled valve units, piezoelectric final control elements (actuators) can also be used, which have a requisite temperature equalization and optionally a requisite force or travel boost. 
     Below, in the description of FIGS. 2-8, only differences from the fuel injection system of FIG. 1 will be addressed. Identical components will not be explained in detail. 
     From FIG. 2, it can be seen that in a modification of the fuel injection system  1 , the pressure booster unit  9  is disposed outside the injector  8  and is now in the region of the pressure reservoir chamber  6 . The structural size of the injector  8  is reduced. The valve  10  can be disposed on the pressure reservoir chamber, and the pressure booster unit can be disposed on the injector. 
     In the fuel injection system of FIG. 3, the pressure reservoir chamber  6  is filled with motor oil or some other suitable pressure fluid  43  from a supply container  44  via the feed line  45  and the pump  42 , in order to trigger the pressure booster unit  9 . The low-pressure side  16  of the pressure means  17  can either be subjected to pressure via the pressure line  47 , or connected to a leakage line  48 . The switchover is attainable by means of the 3/2-way valve  10 . 
     The pressure chamber  13  can be filled with fuel from a further supply container via the check valve  14 , or with the aid of a prefeed pump—as shown—this can be done at a lesser prefeed pressure. The injection takes place as described for FIG.  1 . 
     Alternatively to throttling the fuel in the region of the fuel metering, the second system pressure can be generated using a pressure limiting valve in the form of a check valve  50  in the region of the pressure booster unit (FIG.  4 ). The check valve  50  opens at a pressure of approximately 300 bar. The pressure chamber  13  is filled with fuel from a supply container via the check valve  14 , with the aid of a fuel pump. In this case, at a short stroke of the pressure means  17 , which initially is in its returned position and is then moved in the direction of the bottom of the pressure chamber  13 , the pressure chamber  13  remains in communication with the check valve  50 , so that the pressure in the pressure chamber  13  is limited to 300 bar, so that fuel at this pressure can be carried to the nozzle chamber  20  and the control chamber  19 . The check valve  14  prevents the return flow of compressed fuel in the direction of the fuel pump  2 . 
     At a longer stroke of the pressure means  17  as a consequence of the imposition of pressure on the pressure means  17  with a fluid from the pressure reservoir chamber  6 , the access of the pressure chamber  13  to the leakage line  49  is closed, so that a higher injection pressure is attained. In the main injection, a so-called “boot injection” can thus be performed, along with a pre-injection at low pressure. 
     In a modification of the above exemplary embodiments, a pressure-controlled fuel injection system  51  is shown in FIG.  5 . Once again, a high-pressure pump  52  pumps fuel  53  out of a supply container  54  via a feed line  55  into a pressure reservoir chamber  56 , which stores the fuel  53  at a pressure of 300 to 800 bar and which communicates with individual injectors  58  via individual pressure lines  57 . From the pressure reservoir chamber  56 , the injection pressure of each injector  58  is generated by means of a respective pressure booster unit  59  disposed inside each injector  58 . By means of a valve unit  60  (3/2-way valve), the injection is done under pressure control. A valve member  61  can move, counter to the closing force of a compression spring  62 , away from the valve seat face  63  of the injector housing when a nozzle chamber  64  is filled with fuel at a suitable pressure. In the currentless state of the valve unit  60 , the pressure booster unit  59  is connected to a leakage line  66 . A pressure chamber  67  can be filled via a check valve  68 . 
     By means of a continuous cross-sectional control of the valve  60 , shaping of the course of injection (as in FIG. 1) can be attained. If multi-stage valves are used, it is likewise possible to attain various injection pressure levels by means of different throttle positions. Once again, piezoelectric actuators or magnet actuators are conceivable as actuators. 
     In FIG. 6, the pressure booster unit  59  and the valve unit  60  in a pressure-controlled fuel injection system  51  are located outside the injector  58 , in the region of the pressure reservoir chamber  56 . 
     In the exemplary embodiment of a pressure-controlled fuel injection system  71  in FIG. 7, the generation and boosting of the pressure of fuel  74  delivered from a supply container are achieves with a motor oil as the pressure fluid  72 . The pressure booster unit  73  acts as a coupling element between the fuel delivery and the pressure fluid delivery system. A second system pressure is attained via throttling inside a valve cross section of a valve unit  75  (see the description of FIGS. 1-6 as well). 
     FIG. 8 shows a pressure-controlled fuel injection system  81  which employs a pressure limitation of the fuel compressed In the pressure chamber  82  (see also the analogous stroke-controlled variant in FIG.  4 ). At a short stroke of the pressure means  83 , the pressure in the pressure chamber  82  of the pressure booster unit  84  is limited to approximately 300 bar, since the pressure chamber  82  communicates with a leakage line  87  via a pressure limiting check valve. Upon further motion of the pressure means  83  in the direction of the arrow  85 , this pressure limitation path is closed, and the full injection pressure is generated. 
     This makes a pre-injection at low pressure possible by means of a separate actuation of a valve unit  86 . In a main injection, a boot injection can additionally be generated. The valve unit  86  can be reinforced or triggered directly or hydraulically (control piston and control chamber) by means of magnet actuators (in the event of throttling in the region of the valve seat face, a travel control of the magnet valve must be provided). By the use of a piezoelectric actuator, shaping of the course of injection (a boot injection) in the main injection can also be achieved. This is equally applicable to all the embodiments of the invention. 
     FIG. 9 pertains to a pressure-controlled fuel injection system  91  with an injection nozzle that is modified compared to the exemplary embodiments shown above. Once again, via a fuel pump, fuel or alternatively motor oil is pumped into a pressure reservoir chamber at a pressure of approximately 300 to approximately 300 bar. Beginning at this pressure reservoir chamber, the Injection pressure is generated locally for each cylinder via a pressure booster unit. If motor oil is used as the fluid, the pressure booster unit also acts as a coupler. Via a 3/2-way valve  92  with a cross-sectional control or a piezoelectric actuator, the injection is achieved under pressure control. In the currentless state, the low-pressure side of the pressure booster unit is connected to leaking oil and can be filled via a check valve  93 . By means of throttling in the valve seat of the valve  92 , a second injection pressure can be developed. Instead of the blind bore or seat bore nozzles shown in the above drawings, a vario-nozzle or vario-register nozzle is used. The opening cross section of the nozzle holes that is available is variable. The course of injection can be adapted still better to the requirements of the engine. In the case of a vario-register nozzle, a plurality of rows of nozzle holes can be opened in stages. The triggering for the hydraulic stroke stop  94  of the nozzle can be done both inside the injector  95  and also centrally for all the injectors simultaneously. 
     The foregoing relates 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.