Abstract:
In an injection system for an internal combustion engine, having one fuel pump per engine cylinder to be supplied of the engine, the pump being controlled electronically, having an injection nozzle that is provided with a nozzle needle, and having a connecting line between the fuel pump and the injection nozzle, it is an object for the injection course to be freely selectable. To this end, the injection nozzle is provided with an electronically controlled valve, which is capable of controlling the opening of the nozzle needle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 01/00119 filed on Jan. 13, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an injection system for an internal combustion engine, having one fuel pump per engine cylinder to be supplied, which pump is controlled electronically; having an injection nozzle, which is provided with a nozzle needle; and having a connecting line between the fuel pump and the injection nozzle. 
     2. Description of the Prior Art 
     Such an injection system is an individual-cylinder system, in which the injection pump is driven by a camshaft, for instance. Upon actuation by a cam, the fuel to be injected is put under pressure in the fuel pump and delivered to the injection nozzle. The onset and end of pumping by the fuel pump can be controlled for instance by means of a slide valve, which in a first state connects the pumping chamber of the pump with a return line, so that fuel pumping does not occur, and in a second state closes the connection to the return line, so that a pressure buildup is possible. In this way, the injection onset and also, via a control of the length of the injection event, the injection quantity as well can be controlled. However, the injection pressure is a function of the rpm of the camshaft that drives the pump. The course of injection and a pre-injection can also be varied only in the pump. This leads to restrictions in terms of the pre-injection quantity and the shaping of the course of injection, as well as unacceptable deviations between the various individual cylinders of the engine. 
     The object of the invention is thus to refine a known injection system in such a way that not only the injection quantity and the injection onset but also the injection pressure, course of injection, pre-injection, post-injection and multiple injection can be varied in the desired way. 
     SUMMARY OF THE INVENTION 
     The injection system of the invention has the advantage that by suitable actuation of the electronically controlled valve at the injection nozzle, the fuel volume furnished by the fuel pump can be injected as desired; additional parameters for controlling the course of injection are furnished, which are independent of the onset and end of pumping by the fuel pump. Unlike conventional systems, in which the nozzle needle has opened automatically as soon as a predetermined pressure is exceeded after the onset of pumping by the fuel pump, and the nozzle needle also closes automatically again as soon as a certain minimum pressure toward the end of pumping is undershot, with the injection system of the invention it is now possible to inject essentially independently of the pumping rate of the fuel pump. It is also possible, for the same fuel pump dimensions, to utilize the entire stroke of the pump and thus enhance the performance of the system for the same dimensions. Another advantage is that only slight modifications compared with the conventional systems are necessary. The previously used injection nozzle must merely be replaced by an electronically regulated injection nozzle. 
     In comparison with so-called common rail systems, in which a single fuel pump is used to supply a high-pressure collection chamber, from which the fuel is then injected into the individual cylinders, the system of the invention offers greater operating safety, since in the event of later failure of the fuel pump, because of the modular design of the system only the corresponding cylinder of the engine is affected. The course of injection can be controlled variably in the same way as is possible in a common rail system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in detail herein below with reference to the accompanying drawings in which: 
     FIG. 1 is a schematic, partially sectional view, of one embodiment an injection system of the invention; 
     FIG. 2 is detail II of FIG. 1, on a larger scale; 
     FIG. 3 is a view corresponding to that of FIG. 1 of an injection system in accordance with a second embodiment of the invention; 
     FIG. 4 is a sectional view of an injection nozzle which can be used in an injection system in accordance with a third embodiment of the invention; 
     FIG. 5 shows detail V of FIG. 4, on a larger scale; and 
     FIGS. 6 a - 6   d  are various graphs of characteristic variables that are relevant to the course of injection that is attainable with the injection system of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, an injection system according to the invention is shown in a first embodiment. As its most essential components, it includes a fuel pump  10 , an injection nozzle  12 , and a connecting line  14  between the fuel pump and the injection nozzle. 
     The fuel pump  10  is actuated by a rotating cam  16  and has a pump piston  18 , which is displaced within a pressure chamber  20 . The fuel to be injected is delivered to the fuel pump  10  through a fuel inlet  22 , shown schematically. For return to a fuel tank, a fuel return  24  is provided. Neither the low-pressure system formed by the fuel inlet  22  and a prefeed pump for the fuel nor the pressureless return system formed by the fuel return  24  is shown in the drawing. Nor are various leakage returns  26 , which can be considered to belong to the fuel return  24 , shown in detail. 
     The fuel pump  10  is provided with a control slide  28 , which is actuated by an electronic controlled final control element  30  that communicates with an electronic control unit  32 . The control slide  28  can be adjusted, as a function of instructions from the control unit  32 , by the final control element  30  between an open position, in which the pressure chamber  20  of the fuel pump communicates with the fuel inlet  22  and the fuel return  24 , so that no fuel pumping takes place, and a closed position, in which the communication with the fuel inlet and with the fuel return is closed and a displacement of the pump piston  18  in the pressure chamber  20  causes the fuel located in the pressure chamber  20  to be pumped via the connecting line  14  to the injection nozzle  12 . 
     The injection nozzle  12 , which is provided with a reservoir  13 , has a nozzle needle  34 , which is displaceable between a closed position, in which the furnished fuel cannot emerge from the injection nozzle  12 , and an opened position, in which the furnished fuel is injected into the cylinder of the engine. The nozzle needle  34  is braced on a thrust rod  36  (see FIG.  2 ), which closes off a control pressure chamber  38  on one side. The control pressure chamber  38  is provided with an inlet  40 , which has an inlet throttle  42 , embodied as a bore of small cross section, and an outlet  44 , which likewise has an outlet throttle  46  embodied as a bore of small cross section. The cross section of the outlet throttle  46  is larger than the cross section of the inlet throttle  42 . 
     The outlet  44  from the control pressure chamber  38  is controlled by a valve element  48 , which is adjustable by a final control element  50 , which likewise communicates with the control unit  32 , between a position that closes the outlet  44  and a position that opens the outlet  44 . When the valve element  48  closes the outlet  44 , a fluid delivered via the inlet  40 , typically fuel, is dammed up in the control pressure chamber  38 . As a result, via the thrust rod  36 , a force is exerted on the nozzle needle  34  that keeps the nozzle needle in the closed position, counter to an opening force that is generated by the fuel pressure prevailing at the nozzle needle. Conversely, when the valve element  48  opens the outlet  44 , the fluid dammed up in the control pressure chamber  38  can flow out of this chamber, since the outlet throttle  46  has a larger cross section than the inlet throttle  42 . Thus no further force is presented counter to a displacement of the thrust rod  36 , and the nozzle needle  34  is lifted from its valve seat by the fuel pressure exerted on it, so that the fuel can be injected into the cylinder. 
     The mode of operation of the injection system described is as follows: The injection event is initiated with the activation of the final control element  30 . The final control element displaces the control slide  28  into the position in which the communication between the pressure chamber and both the fuel inlet and the fuel return is closed, so that the fuel pump pumps. As a result, fuel in the connecting line  14  and in the injection nozzle  12  is compressed by the pump piston  18 . The nozzle needle  34  remains in its closed position until such time as the desired pressure level is attained; the time between the closure of the control slide  28  and the opening of the nozzle needle  34  thus defines the available injection pressure. When the injection event is to begin, the outlet  44  is opened by the valve element  48 , so that the nozzle needle  34  can lift from its valve seat. By means of the actuation of the valve element  48  independently of the control slide  28 , a pre-injection, a main injection with an arbitrary course of injection, and a post-injection can be controlled. The various characteristic variables that are relevant to these cases are shown in the graphs in FIGS. 6 a - 6   d.    
     In FIG. 6 a , the current through the final control element  30  is shown as a function of the angle of rotation of the crankshaft of the internal combustion engine that is to be supplied with fuel. In FIG. 6 b , the current through the final control element  50  of the injection nozzle is shown as a function of the angle of crankshaft rotation. In FIG. 6 c , the stroke of the control slide  28  is shown as a function of the angle of crankshaft rotation. Finally, in FIG. 6 d , the stroke of the valve element  48  is shown as a function of the angle of crankshaft rotation. 
     It can be seen clearly from the graphs that the control of the valve element  48  can be done independently of the control of the control slide  28 , so that the desired course of injection can be selected freely. 
     In FIG. 3, an injection system in accordance with a second embodiment is shown. It differs from the injection system shown in FIG. 1 in that a high-pressure collection chamber  21  is disposed in the interior of the fuel pump  10 , between the pump piston  18  and the control slide  28 . The high-pressure collection chamber  21  functions like a pressure reservoir, so that an even greater time lag between the onset of pumping by the fuel pump  10  and the opening of the nozzle needle  34  of the injection nozzle  12  is possible. 
     In FIGS. 4 and 5, an injection nozzle  12  for an injection system in a third embodiment is shown. Instead of the valve element  48 , a valve slide  52  is used do here, forming a 3/2-way valve. Once again, an inlet throttle  42  and an outlet throttle  46  are provided, and the inlet to the nozzle needle  34  is opened upon the opening of the valve slide  52 . In the closed state of the valve slide  52 , the inlet to the nozzle needle  34  and the nozzle chamber overall are relieved by the valve slide  52  to the fuel return  24 . The advantage of this embodiment is that the injection nozzle is subjected to the fuel pressure only during the injection. 
     The foregoing relates to a preferred exemplary embodiment 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.