Abstract:
The invention relates to a high-pressure injection system, in particular for auto-igniting internal combustion engines, with at least one high pressure pump and a high pressure reservoir, through which at least one fuel injector is supplied with a fuel under pressure. The high-pressure injection system comprises at least one pressure booster unit which has at least two pressure boosters, each with a high pressure piston which can be driven independently of the other.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP2008/055456 filed on May 5, 2008. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a high-pressure injection system, in particular for auto-igniting internal combustion engines. 
     2. Description of the Prior Art 
     European Patent Disclosure EP 0 711 914 A1 relates to a pressure-controlled fuel injection system, in which, with the aid of a high-pressure pump, fuel is compressed to a first high fuel pressure of approximately 1200 bar and stored in a first pressure reservoir. The fuel under high pressure is also supplied to a second pressure reservoir, in which, by regulation of its fuel delivery by means of a 2/2-way valve, a second high fuel pressure of approximately 400 bar is maintained. Via a valve control unit, either the lower or the higher fuel pressure is conducted into the nozzle chamber of an injector. There, a spring-loaded valve body is lifted from its valve seat by the pressure, so that fuel can emerge from the nozzle opening into the combustion chamber. 
     A disadvantage of this known fuel injection system is the fact that all the fuel must first be compressed to the higher pressure level and then some of the fuel is relieved again to the lower pressure level. Moreover, the high-pressure pump, since it is driven by the camshaft of the engine, is constantly in operation, even when the desired pressure in the respective pressure reservoir has already been built up. This permanent generation of high pressure and the ensuing relief to the low-pressure level stand in the way of improved efficiency. 
     The high-pressure fuel pumps used in the field of self-igniting internal combustion engines are currently capable of building up pressures of up to approximately 2200 bar. Pressures beyond that are possible either with two-stage high-pressure pumps or with additional pressure boosters outside or inside the fuel injectors. Two-stage high-pressure pumps require markedly greater installation space and are not compatible with current systems. Moreover, the mechanical load in terms of pump development is considered critical. Internal and external pressure boosters are currently used solely as local pressure boosters for individual injectors; that is, per injector, one pressure booster is in use. In terms of expense, this first means a large number of additional components, and in terms of function, it means poor efficiency in pressure-boosted injection of small quantities, since for each pressure boosting event, there must be a minimum turnover in the control quantity in the pressure booster. One such central pressure booster is known for instance from European Patent Disclosure EP 1 125 046 B1. 
     SUMMARY OF THE INVENTION 
     According to the invention, a pressure booster is proposed that is an individual, separate structural unit and is approximately the same size as, and takes on the function of, the pressure reservoir that is conventionally used. In the conventional pressure reservoir, a conventional high-pressure pump represents a currently common pressure level on the order of magnitude of approximately 2000 bar, which will hereinafter be called medium pressure. The pressure booster proposed according to the invention advantageously has at least two pistons for attaining the pressure boosting, which are operated in alternation and thus enable a continuous supply at high pressure, that is, at a pressure level of &gt;2500 bar. The supplied quantity can therefore be made available to the individual fuel injectors even without a large high-pressure reservoir, since a pressure drop from withdrawal at the injector can be maximally compensated for by immediate replenishment. 
     Thus the complex separate pressure boosting for each individual fuel injector provided in a fuel injection system is eliminated, so that functionally, the significant advantage is attained that, at injection pressures below the maximum pressure of the high-pressure pump, the required quantity can be supplied to the individual fuel injectors without activation of the pressure booster. Precisely for lesser injection quantities to be introduced into the combustion chambers of self-igniting internal combustion engines, this means a pronounced increase in the hydraulic efficiency, because of the elimination of the previously necessary pressure booster control quantity. 
     Alternatively, a simplified version of the pressure booster with only one on-off valve and one pressure booster piston each is equally conceivable, for the case where the restoration time of the pressure booster piston is sufficiently short for the required engine rpm and thus for the activation frequency of the pressure booster. In that case, a different boosting ratio of the pressure booster may be necessary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in further detail below in conjunction with the drawings, in which: 
       Shown are: 
         FIG. 1  shows a first embodiment of the high-pressure injection system, proposed according to the invention, with a pressure booster unit; 
         FIG. 2  shows a second embodiment of the high-pressure injection system, proposed according to the invention, having a pressure booster unit with which an intermediate pressure reservoir and a high-pressure reservoir are integrated; 
         FIG. 3  is a sketch of the pressure booster unit with two pressure boosters; 
         FIG. 4  shows a further embodiment of the pressure booster unit proposed according to the invention (without a high-pressure reservoir); 
         FIG. 5  shows a pressure booster unit (with an integrated high-pressure reservoir); 
         FIG. 6  shows the alternative mode of operation of the pressure booster pistons with synchronous injection; 
         FIG. 7  shows synchronous injections in the synchronous mode of operation of the pressure booster pistons; 
         FIG. 8  shows the alternating mode of operation of pressure booster pistons with asynchronous injection; and 
         FIGS. 9.1  through  9 . 5  shows system images for the high-pressure injection system, proposed according to the invention, with variant forms of piping. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the high-pressure injection system can be seen in  FIG. 1 . The high-pressure injection system as shown in  FIG. 1  includes, besides a tank  12 , a high-pressure pump  14 . The high-pressure pump acts upon a pressure booster unit  16 , which in this first embodiment includes both an intermediate rail  18  and an optionally activatable pressure booster  24 . The pressure booster unit  16  in turn acts upon an externally disposed high-pressure reservoir  20 , which in turn has a number of high-pressure connections  26 . Via the high-pressure connections  26 , which are provided on the high-pressure reservoir  20  in a number that corresponds to the number of fuel injectors  22  to be supplied with fuel, the internal combustion engine, not shown in  FIG. 1 , is supplied. Via the dashed lines from the fuel injector  22  or from the pressure booster unit  16 , a control or leakage quantity is returned to the tank  12  of the high-pressure injection system  10 . 
       FIG. 2  shows a second embodiment of the high-pressure injection system proposed according to the invention, in which in a distinction from what is shown in  FIG. 1 , the pressure booster unit  16  includes the intermediate rail  18 , the optionally activatable pressure booster  24 , and the high-pressure reservoir  20  as an integrated component. In that case, the high-pressure connections  26 , corresponding in number to the number of fuel injectors  22  to be supplied with fuel, are provided on the pressure booster unit  16 . As can be seen from  FIG. 2 , a leakage or control quantity, both from the pressure booster unit  16  and from the at least one fuel injector  22 , is returned to the tank  12  of the high-pressure injection system  10  via the lines represented by dashed lines. 
       FIG. 3  shows the schematic makeup of the pressure booster; two such boosters are installed in each of the pressure booster units shown in  FIGS. 1 and 2 . 
     As can be seen from  FIG. 3 , a pressure booster  24 , of which at least one is installed in a pressure booster unit  16 , includes a base body  30 . In the base body  30 , there are pressure booster pistons  32 ,  33 . The pressure booster units  16  shown in  FIGS. 1 and 2  each include two pressure boosters  24 . 
     The pressure booster piston  32  is disposed in the base body  30  and has both a first piston part  34  of larger diameter and a second piston part  36  of lesser diameter. An annularly embodied collar  38 , on which a restoring spring  40  is braced, is located on the first pressure piston part  34 . The restoring spring  40  is also braced on an annular face of a piston guide body  42 . 
     Both a high-pressure valve  44  and a filling valve  46  are located in the base body  30  of the pressure booster  24  shown in  FIG. 3 . These two valves  44 ,  46  are preferably embodied as check valves. The high-pressure valve  44  is located in a reservoir supply line  54  that communicates with a high-pressure chamber  60 . The high-pressure chamber  60  is defined on one side by the piston guide body  42  and on the other side by a high-pressure face  64 . 
     The filling valve  46  is located in a hydraulic line which as shown in  FIG. 3  connects a control chamber  62 , via an on-off valve  50  and a bypass  68 , to a reservoir volume  58 . The on-off valve  50 , which may for instance be embodied as a 3/2-way valve, for instance as an on-off valve actuated by a magnet valve, is also integrated with the base body  30  of the pressure booster  24  shown in  FIG. 3 . 
     Extending from the base body  30  of the pressure booster  24  as shown in  FIG. 3  are a pressure booster return  56 , located downstream of the on-off valve  50 ; the reservoir supply line  54  with the integrated high-pressure valve  44 , which extends to the high-pressure reservoir  20  in the system overviews in  FIGS. 1 and 2 ; and a pressure booster inlet  52 , which is acted upon by way of the high-pressure pump  14  shown in  FIGS. 1 and 2 . It can also be seen from  FIG. 3  that the reservoir volume  58 , which is also called a medium-pressure reservoir, communicates with the control chamber  62  via a bypass  68 . 
     At injection pressures below the maximum supply pressure of the high-pressure pump  14 , what is here called a medium pressure is supplied by the high-pressure pump  14 , via the pressure booster inlet  52 , into the reservoir volume  58 , which is embodied in one or more parts, and onward via the filling valve  46  and the high-pressure valve  44  directly to the reservoir supply line  54 . From there, it reaches either an external high-pressure reservoir  20 , shown in  FIG. 1 , or, —via the internal high-pressure reservoir—the fuel injectors  22 , as shown in  FIG. 2 . 
     In this case, the pressure booster  24  as schematically shown in  FIG. 3  is operated in the bypass mode, in which no pressure boosting is necessary, and therefore no significant losses of efficiency occur. In the bypass mode, supply is done simultaneously through all the available pressure boosters  24  of a pressure booster unit  16 —as shown in  FIGS. 1 and 2 . 
     If pressure boosting is necessary, the pressure boosters  24  of the pressure booster unit  16  can be used in alternation or simultaneously. In each of these cases, the corresponding on-off valve  50 , which is preferably a 3/2-way valve, is switched. The control chamber  62  of the pressure booster piston  32  communicates with the pressure booster return  56  as a consequence of the activation of the on-off valve  50  and is accordingly pressure-relieved. As a result, the pressure in the high-pressure chamber  60  of the pressure booster  24  increases, until a force equilibrium has been established between the high pressure at the high-pressure face  64  of the high-pressure piston  32  and the force generated by the restoring spring  40 , on the one hand, and the medium pressure at the medium-pressure face  66  of the pressure booster pistons  32 ,  33 , on the other. 
     Preferably, the boosting ratio i, defined by the two pressure faces  64  and  66 , is equivalent to the quotient of the desired maximum pressure, which is supplied to the reservoir supply line  54 , and the supply pressure of the high-pressure pump. Thus the high-pressure quantity is replenished by the high-pressure valve  44  when the pressure at the high-pressure connection, that is, in the reservoir supply line  54 , drops as the result of a withdrawal of quantity. Via the filling valve  46 , the communication with the reservoir volume  58  is closed. 
     Upon deactivation of the on-off valve  50 , the control chamber  62  of the high-pressure piston  32  is made to communicate with the reservoir volume  58 , and as a result the pressure in the control chamber  62  rises, and in a hydraulic force equilibrium, the pressure booster piston  32 ,  33  is positioned at its stop limitation  48  by the spring force of the restoring spring  40 . 
     Preferably, the activation of the on-off valves  50 , each associated with one pressure booster  24 , is synchronized with the injections, so that one supply stroke of the pressure booster  24  ensues per cylinder of the engine to be supplied with fuel and per 720° of crankshaft angle, in the case of a 4-cycle internal combustion engine. It is correspondingly assured that the restoring time of each pressure booster piston  32  and  33 , respectively, of the at least one pressure booster  24  is sufficiently short that, in the case of a pressure booster unit  16  equipped with two pressure boosters  24 , supply can be done at every other injection. 
     The pressure booster unit  16  as shown in  FIGS. 1 and 2 , besides the intermediate reservoir (intermediate rail), preferably includes two pressure boosters  24  and optionally—as shown in the embodiment of FIG.  2 —a high-pressure reservoir  20  (high-pressure rail), which is integrated with the pressure booster unit  16 . 
     In  FIGS. 4 and 5 , various embodiments of pressure booster units, which are shown only schematically in  FIGS. 1 and 2 , are represented. The intermediate reservoir  18  (intermediate rail) is not necessarily a separate component, but instead is divided into a reservoir volume  58  (see  FIG. 3 ) of the preferably two pressure boosters  24  constricted inside one pressure booster unit  16 . 
     As seen for instance from  FIG. 4 , the pressure booster unit  16  can include a U-shaped central body  94 , which has reservoir pots  92  in which the individual pressure boosters  24  of the pressure booster unit  16  are made. On each face end of the central body  94  are a first on-off unit  84  and a second on-off unit  86 , respectively, each embodied as a 3/2-way valve for an on-off valve  50 . Laterally on the U-shaped central body  94  of the pressure booster unit  16 , there are connections  82 , which are the connections  82  shown in  FIG. 3 , namely the pressure booster inlet  52 , the reservoir supply line  54 , and the pressure booster return  56 . For instance, the high-pressure pump  14  shown in  FIG. 1  is connected to the pressure booster inlet  52 —see also reference numeral  98 ; see reference numeral  98  in  FIG. 1 . The connections  82  at the U-shaped central body  94  of the pressure booster unit  16  also, as shown in  FIG. 4 , include high-pressure connections  100 , which lead for instance to the high-pressure reservoir  20  shown in  FIG. 1 . 
     It can also be seen from  FIG. 4  that the two pressure boosters  24 , of which one pressure booster  24  has the pressure booster piston  32  and the other pressure booster  24  has the pressure booster piston  33 , are disposed parallel to one another. The pressure booster  24  having the pressure booster piston  32  is inactive; the other pressure booster  24  having the pressure booster piston  33  is active. Both a pressure regulating valve  102  and a pressure sensor  104  are located on the central body  94  of the pressure booster unit  16 . It can also be seen from  FIG. 4  that the active one of the two pressure boosters  24  carries fuel, compressed in accordance with the pressure boosting ratio i, to the high-pressure reservoir  20  shown in  FIG. 1  via the respective reservoir supply lines  54 . The construction of the pressure boosters  24  shown in the embodiment of  FIG. 4  is essentially equivalent to what is shown for the pressure boosters  24  in  FIG. 3 . 
     The pressure booster unit  16  in the embodiment shown in  FIG. 5  likewise has connections  82 , which represent the pressure booster inlet  52  and the reservoir supply line  54 . The pressure booster return is not shown. 
     In  FIGS. 4 and 5 , pressure booster units  16  are shown in each case that have a reduced structural length, which is achieved because of the U-shaped, one-piece central body  94 . Also in the embodiments of  FIGS. 4 and 5 , connection possibilities are provided on the face end of the one-piece central body for the pressure sensor  104  and the pressure regulating valve  102  which is shown schematically there. 
     While  FIG. 4  represents a variant of the first embodiment of  FIG. 1 ,  FIG. 5  represents a variant of the second embodiment of  FIG. 2 , with an integrated high-pressure reservoir  20 . 
     It can be seen from  FIG. 5  for example that the pressure booster unit  16  has a very compact structure, which is attained by means of the one-piece central body  94 . In this embodiment of the pressure booster unit  16  as well, in accordance with what is schematically shown in  FIG. 1 , two pressure reservoir pots  92  are provided, which are placed next to one another. Diametrically opposite the two pressure reservoir pots  92  on the one-piece central body  94  are the first on-off unit  84  and the second on-off unit  86 , which can be embodied for instance as magnet valves; see reference numeral  50  in  FIG. 3 . 
     In  FIG. 5 , an embodiment of the pressure booster unit  16  with an integrated high-pressure reservoir of  FIG. 4  can be seen. 
     Also from  FIG. 5 , a pressure booster unit  16  with a central body  94 , here embodied in one piece analogously to  FIG. 4 , can also be seen. In this embodiment, the two pressure reservoir pots  92  and the first on-off unit  84  and the second on-off unit  86  are all disposed side by side on the one-piece central body  94 . In the view in  FIG. 5 , reference numeral  98  indicates a pump connection analogous to reference numeral  52  in the embodiment of  FIG. 3  that designates the pressure booster unit inlet. Reference numeral  100 , conversely, identifies a high-pressure connection, analogous to reference numeral  54  in the embodiment of  FIG. 3 ; the fuel injectors or the high-pressure lines that lead to them are connected there. 
     The pressure booster unit  16  in the embodiment shown in  FIG. 5  is a pressure booster unit with which a 4-cylinder internal combustion engine, for instance, with fuel at system pressure can be supplied. The connections  82  are located laterally on the one-piece central body  94 . Together with the high-pressure connections  82  and  100  disposed laterally on the central body  94 , it is possible for instance for four fuel injectors, or four high-pressure lines that lead to four fuel injectors, to be connected to the pressure booster unit  16  shown in  FIG. 5 . 
       FIG. 6  shows an alternating mode of operation of two pressure booster pistons with synchronous injection. 
     From  FIG. 6 , it can be seen that a piston stroke h of a first pressure booster piston  32  and of a second pressure booster piston  33 —the latter indicated by dashed lines—is plotted over time t. Reference numeral  122  represents the activation of each fuel injector  22 , and the fuel injectors  22  each have an injection characteristic that for instance extends in ramplike fashion, while the fuel is introduced into the various cylinders of the engine. Instead of a ramplike injection characteristic, multiple injections can also be made, or arbitrary further injection strategies be implemented. As can be seen from  FIG. 6 , stroke courses  112  and  114  in an alternating mode of operation  110  of the respective pressure booster pistons  32 ,  33  can overlap one another slightly. While the first stroke course  112  and the second stroke course  114  of the first pressure booster piston  32  is represented by solid lines, the first stroke course  112  and the second stroke course  114  of the second pressure booster piston  33  is by comparison represented by dashed lines. The prerequisite for the alternating mode of operation, as indicated by reference numeral  110 , of the pressure booster unit  16  is that the pressure booster unit  16  shown schematically in  FIGS. 1 and 2  includes two pressure boosters  24  as shown in  FIG. 3 . 
     From  FIG. 7 , a synchronous mode of operation of a pressure booster unit  16  with two pressure boosters  24  can be seen. From the stroke courses of the first stroke  112  and the second stroke  114  shown in  FIG. 7 , it can be seen that in this case, the first high-pressure piston  32  and the second high-pressure piston  33 —the latter indicated by dashed lines—are both operated synchronously. In this case, the respective first stroke courses  112  and second stroke courses  114  each coincide. Because of the overlapping supply strokes  112  and  114  of the two pressure booster pistons  32  and  33 , respectively, the supply quantity can be increased, and the pressure drop in the high-pressure reservoir  20  of the high-pressure injection system  10  in the schematic overview drawings in  FIGS. 1 and 2  can be further reduced. The individual injection events are preferably effected synchronously with the supply—as indicated in FIG.  7 —in order thereby to keep the pressure drop slight. As is shown in conjunction with  FIG. 8 , which shows an alternating mode of operation of the pressure booster pistons with asynchronous injection, the injections can also if necessary be made between the individual pressure booster strokes  112  and  114  of the first pressure booster piston  32  and the second pressure booster piston  33 , respectively. To that end, replenishment may be provided in the intervals between the individual injection events. In a distinction from what is shown in  FIG. 7 , the first pressure booster piston  32  and the second pressure booster piston  33  execute a first stroke  112  in the intervals between injections of fuel injectors  22 , which here are shown emphasized as examples. A further stroke  114  may coincide in part, entirely, or not at all with an injection. In this connection, it is definitive that the first stroke  112  does not coincide with the injection but instead takes place in an interval between injections. 
     As can be seen from the sequence of  FIGS. 9.1  through  9 . 5 , the pressure booster unit  16  as schematically shown in  FIGS. 1 and 2  can be made to communicate hydraulically with the fuel injectors in various ways. 
       FIG. 9.1  shows that the high-pressure pump  14  subjects the pressure booster unit  16  to fuel at high pressure, at a pressure level of approximately 2000 bar. The pressure booster unit  16  in turn subjects the externally disposed high-pressure reservoir  20  to a pressure which is elevated in accordance with the boosting ratio i of the two pressure boosters  24 ;  FIG. 9.1  involves an externally disposed high-pressure reservoir  20 . From this high-pressure reservoir, individual high-pressure lines  140  lead to the various fuel injectors  22 . In this variant form of piping in  FIG. 9.1 , they supply a 6-cylinder internal combustion engine. 
     From  FIG. 9.2 , a variant form of piping can be seen that is slightly modified compared to the variant in  FIG. 9.1 . In the embodiment of  FIG. 9.2 , the high-pressure pump  14  acts on the pressure booster unit  16 , which acts in turn on the external high-pressure reservoir  20 . In  FIG. 9.2 , a ring line  142  represented by individual connecting pieces  144  extends between the various fuel injectors  22 . As a result, individual high-pressure lines  140 —as used in FIG.  9 . 1 —associated with each of the individual fuel injectors  22  can be avoided. The ring line  142  for connecting the fuel injectors  22  has a major advantage from a hydraulic standpoint, since the reservoir volume in the fuel injectors  22 , with only slight three-dimensional spacings, reduces pressure drops and resultant pressure fluctuations. If the rail, that is, the high-pressure reservoir  20 , disposed externally relative to the pressure booster unit  16  in  FIGS. 9.1  and  9 . 2  is dispensed with, then via the ring line  142 , the number of necessary connections to the pressure booster unit  16  can furthermore be reduced in comparison to the variant embodiment of  FIG. 9.3 ; see for instance the embodiments in  FIGS. 9.4  and  9 . 5 . 
     In the embodiment of the piping layout shown in  FIG. 9.3 , at the pressure booster unit  16  shown schematically there, six individual high-pressure lines  140  are connected to the individual fuel injectors  22 , while in the pressure booster units  16  in the embodiments of  FIGS. 9.4  and  9 . 5 , compared with the embodiment of  FIG. 9.3 ,  9 . 5 , only two individual high-pressure lines  140  have to be connected, since the fuel injectors  22  in turn communicate with one another via connecting pieces  144  inside the ring line  142 . In the variant form of piping shown in  FIG. 9.5 , the high-pressure reservoir  20  is disposed externally relative to the pressure booster unit  16  and acts directly on a connecting piece  144  of the ring line  142  between the fuel injectors  22 . 
     The foregoing relates to the 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.