Abstract:
The invention relates to a method for shaping the injection pressure course ( 27 ) in injectors, which are used for instance in injection devices of injection systems in motor vehicles. The injection device includes a pump part ( 1 ) and an injection nozzle part ( 2 ). The pump part ( 1 ) and injection nozzle part ( 2 ) communicate with one another via a high-pressure line ( 3 ). Control valves ( 8, 10 ) which are triggered by means of an actuator ( 9 ) are contained in the pump part ( 1 ). By the triggering by means of the actuator ( 9 ), injection parameters during the preinjection phase ( 28 ), pressure buildup phase ( 29 ) and main injection phase ( 30 ) are determined.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 01/01019 filed on Mar. 20, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method and a device for shaping the injection pressure course in injectors. Injectors and injection systems in which the injectors are used are employed to supply fuel to internal combustion engines of motor vehicles. 
     2. Prior Art 
     In the procedure of the prior art, in order to vary the course of the injection pressure during the injection, the volume of fuel positively displaced by the pump piston in the pump part of an injector housing is in part blown out via a slightly open control valve. Without the opening of the control valve, a continuous increase in the injection pressure would occur. This procedure is known by the abbreviation CCRS (for Current Controlled Rate Shaping), in which magnet valves, in particular, are used as units that actuate the control valves. 
     In another embodiment representing the prior art, a magnet valve is provided which serves the purpose of pressure buildup, along with a further pressure valve, which as a valve to be located downstream serves solely to regulate the pressure level during the pressure buildup phase (boot phase). 
     With the embodiments of the prior art, only individual phases of the injection pressure course can be regulated during the injection. A more-extensive shaping of the injection pressure course, along with a substantially more-compact structural shape of injectors, is not possible since the embodiments described here use magnet valves that take up space on the one hand and on the other need further magnet valves in order to shape the injection pressure course in more detail. 
     SUMMARY OF THE INVENTION 
     With the method and the device proposed according to the invention, both the duration of the preinjection phase and the duration of the pressure buildup phase can be determined by the triggering by means of an actuator. Furthermore, with the method proposed, specifying the pressure to various pressure level values during the pressure buildup phase is possible. The same is analogously true for setting the height of the allowable and mechanical still tolerable maximum pressure toward the end of the main injection phase. Depending on the load-bearing capacity of the mechanical components, a pressure limitation toward the end of the main injection phase can be adapted to the applicable conditions of use of the injection system. It is furthermore possible with the method proposed according to the invention to assure that a diversion rate adapted variably to given conditions of use can be set. Depending on the intended use, the course of the pressure reduction can be preselected such that the instant of the end of the main injection and the instant of the onset of the pressure reduction phase can each be adapted individually. 
     With the method proposed according to the invention, the pump part of an injector system can be designed such that merely a single pump can be used for various designs of internal combustion engines. The pressure buildup phase for instance, which directly follows the preinjection phase, can be initiated by an actuator control in accordance with the intended use, regardless of how the nozzles and pump pistons are designed. 
     The course of the pressure in the pressure buildup phase is also independent of the load and the torque in the instantaneous operating state of the engine and can for instance be preselected precisely such that the pressure in the pressure buildup phase is just above the opening pressure for the nozzle needle received movably in the injector housing. 
     Another advantage attainable by means of the method of the invention is that the control valves can be moved into the sealing seat for the pressure buildup phase. As a result, it is possible to expand the actuator stroke tolerances, which makes the production of the actuator less expensive, since the protection against leakage losses for fuel that is at high pressure is assured by means of the control valves that have moved into their sealing position. 
     Triggering the control valves by means of a piezoelectric actuator makes it possible to dispense with magnet valves which take up greater space, and as a result the injector can be designed with an extremely compact construction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in further detail below in conjunction with the drawings, in which: 
     FIG. 1 illustrates the pump part of an injector, which communicates by means of a high-pressure line with the injection nozzle part of the injector; 
     FIG. 2 illustrates the disposition of the control valves in the pump part of the injector; 
     FIG. 3 is a fragmentary sectional view of on the coupling chamber; 
     FIG. 4 graphically illustrates the stroke and pressure courses for the components of the injection system that accomplish the injection event; and 
     FIG. 5 illustrates the nozzle needle stroke length along with the injection pressure course that can be shaped, in each case plotted over the time axis and compared with one another. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The pump part  1  communicates with the injection nozzle part of the injector via the high-pressure line  3 . In the pump part  1 , the pump chamber  4  is acted upon by a piston  5 . Two control valves  8  and  10  are associated with the high-pressure line  3  and disposed downstream of the pump chamber  4 . The control valves  8  and  10  are each acted upon by a respective force storing means  12  or  13 , and the force storing means  12  or  13  are adapted to the desired opening characteristic of the two control valves  8  and  10 , respectively. The control valves  8  and  10  communicate with respective pressure chambers  6  that have a lower pressure level, into which chambers excess blown-off fuel can be diverted. The fuel tank of a motor vehicle, for instance, can be considered as an example of such lower-pressure-level pressure chambers. 
     An equal-pressure valve  7  is assigned to one of the control valves  8  and  10 , specifically in the view shown in FIG. 1 to the control valve  10 ; this equal-pressure valve is provided in the return line from the second control valve  10  into the low-pressure chamber  6 , or in other words into the supply line to the fuel tank. As an alternative, it is conceivable to dispose the equal-pressure valve  7  upstream of the control valve  10 . By that means, the control valve  10 , because less pressure is exerted on it, could be designed in a more lightweight embodiment. The two control valves  8  and  10  are acted upon by separate force storing means  12  and  13 , respectively, by which the opening characteristic of the first and second control valves  8 ,  10  can be set. A coupling chamber  11  is provided above the two control valves  8  and  10 ; above the coupling chamber  11 , an actuator  9  is provided—preferably embodied as a piezoelectric actuator with which extremely fast switching times are attainable—with which the control parts of the first and second control valves  8  and  10  can be triggered. The use of a piezoelectric actuator instead of magnet valves makes it possible to embody the pump part  1  of the injector of the injection system extremely compactly. 
     The high-pressure line  3  for transporting the fuel that is at high pressure leads from the pump part  1  to the injection nozzle part  2  and discharges into a control chamber  15 , which surrounds the nozzle needle  14  of the injector. The tip of the nozzle needle  14  forms the nozzle  16 , which discharges into the corresponding combustion chambers of the engine. 
     FIG. 2 shows the disposition of the control valves in the pump part of the injector. 
     The motion of the piston  5  causes a pressure increase of the incompressible fuel medium. Via the supply line  18 , the fuel that is at high pressure communicates with chambers, surrounding the control parts, of the control valves  8  and  10 . Each of the control valves  8  and  10  is provided with a respective force storing means, with which the control part of valves  8  and  10  can be kept open in prestressed fashion. The control chamber of the second control valve  10  communicates with the equal-pressure valve  7 , by whose prestressing the diversion rate can be kept variable. Both the various piston parts and the hollow chambers in which the force storing means  12 ,  13  of the two control valves  8  and  10  are received communicate, via outlet lines  17  and  20 , respectively, with the low-pressure chambers  6 , such as the fuel tank, into which the excess fuel can be diverted. 
     As shown in FIG. 1, the control parts of the control valves  8 ,  10  can be moved into different partly open positions by the triggering via the actuator  9 . In the applicable open position or partly open position or closed position—for instance of the second control valve  10 , triggerable by the actuator  9 —a certain fuel quantity, corresponding to the opening cross section uncovered, can then flow out during a likewise preselectable period of time, for instance into the fuel tank  6 , and as a result the injection pressure can be modeled accordingly. 
     FIG. 3 shows the plan view of the arrangement in FIG.  2 . 
     The compact construction of the pump part  1  and injection nozzle part  2  is due to the course of the high-pressure line  3  between the first and second control valves  8  and  10 . Dashed lines show the control chambers surrounding the control valves  8  and  10 . The connecting line  21  from the second control valve  10  to the equal-pressure valve  7  is also shown in dashed lines. From the relative positions, visible in the plan view, of the high-pressure line  3 , the two control valves  8 ,  10 , and the equal-pressure valve  7 , the compact design of the injector is apparent. 
     FIG. 4 shows the various stroke and pressure courses at the components that bring about the injection event in the internal combustion engine. These courses can be subdivided into a preinjection phase  28 , a pressure buildup phase  29 , and a main injection phase  30 . These are followed by a pressure reduction phase  35 . as shown in FIG.  5 . The pressure established in the coupling chamber  11 , shown in graph  23 , is a direct replica of the stroke course of the actuator  9  shown in the first graph  22 . 
     In the graphs  24  and  25 , the stroke lengths that are established in the control valves  8 ,  10  are each plotted over the time axis. Accordingly, with the first control valve  8 , the preinjection phase and the main load of the ensuing pressure buildup phase  29  as well as of the main injection phase  30  are accomplished. The oscillation range of the control part in the first control valve  8 , located in graph  24  between the end of the preinjection phase  28  and the onset of the pressure buildup phase  29 , is represented by an undulating line. 
     From graph  25 , which shows the stroke length of the control part in the second control valve  10 , it can be seen that the control part of this control valve  10  remains unactuated during the preinjection phase  28  and the pressure buildup phase  29 ; for that length of time, the stroke length is equal to zero. Not until the onset of the main injection phase  30  is the second control valve  10  triggered by means of the actuator  9  so that it contributes accordingly to the desired pressure level 34.1, 34.2, 34.3 (FIG. 5) during the main injection phase  30  to increase the pressure in the maximum pressure phase of the injection event. 
     In the graph shown at the bottom in FIG. 4, the nozzle needle stroke length  26  and the injection pressure course  27  during the preinjection phase  28 , the pressure buildup phase  29  (boot phase) and the main injection phase  30  are shown, and in FIG. 5 the pressure reduction phase  35  is shown. With respect to the injection pressure course  27 , it can be seen from a comparison of the stroke length courses  24  and  25  of the two control valves Band  10 , respectively, that the pressure increase toward the end of the main injection phase  30  is effected by triggering of the second control valve  10  into its sealing closing position, so that the bypass to the low-pressure chamber  6 —that is, the fuel tank—is closed, and the maximum pressure occurs at the nozzle  16  (FIG.  1 ). The pressure increase during the injection pressure course  27  toward the end of the main injection phase  30 , and its level 34.1, 34.2, and 34.3 (see FIG.  5 ), are attained solely by the second control valve  10 ; the nozzle needle stroke  26  remains constant during the pressure buildup phase  29  and the main injection phase  30 . 
     FIG. 5 shows the nozzle needle stroke  26 , plotted over the time axis, along with the injection pressure course  27  that can be shaped. 
     The injection pressure course  27  shown in the bottom graph of FIG. 4 is shown in further detail in FIG.  5 . Reference numeral  31  indicates the duration of the preinjection phase  28 ; the preinjection phase  28  is followed by the pressure buildup phase  29 , in which the various pressure levels  32 . 1 ,  32 . 2  and  32 . 3  can be set as shown in FIG.  5 . With the settability of the pressure level, it is possible with one injector to meet the requirements of the most various designs of internal combustion engines. Application-specific settings can be made, so that by the flexible triggerability by means of the actuator  9 , one component can be adapted to various possible uses, so that the number of variants required can be reduced drastically. 
     Reference numeral  33 , shown in FIG. 5, indicates the duration of the pressure buildup phase  29 , but with more detail than is shown by  29  in FIG.  4 . The pressure buildup phase  29 , also called the boot phase, merges with the main injection phase  30 , as shown in FIG.  4 . As shown in FIG. 5, this phase can be increased by means of a further steady pressure increase  34 —beginning at a pressure attained in the pressure buildup phase  29 —to a preselectable maximum pressure level  34 . 1 ,  34 . 2 ,  34 . 3 . 
     The applicable pressure level  34 . 1 ,  34 . 2  and  34 . 3  can be preset by means of the second control valve  10 . By opening of the return line, in which the equal-pressure valve  7  is received, the fuel can flow out into the low-pressure chamber  6 , that is, into the fuel tank. By means of the setting of the pressure level  34 . 1 ,  34 . 2  and  34 . 3 , the maximum pressure can be set to suit requirements, so that the mechanical components of the injector can be protected against damage from excessively high incident pressures. 
     Furthermore, because of the actuator control effected by a piezoelectric actuator, independently of the rpm and load course, a variable course, as indicated by  36  can be obtained during the pressure reduction phase  35 . The course of the pressure reduction can be adapted to individual requirements of the particular intended use by means of varying the slope  36 . 
     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.