Patent Publication Number: US-10330063-B2

Title: Fuel injector

Description:
This application is a 35 U.S.C. § 371 National Stage Application of PCT/EP2016/054285, filed on Mar. 1, 2016, which claims the benefit of priority to Serial No. DE 10 2015 207 307.6, filed on Apr. 22, 2015 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to a fuel injector, in particular a common rail injector, as disclosed herein. 
     A fuel injector as disclosed herein is known from EP 1 042 603 B1. The known fuel injector has within its injector housing a sensor which is arranged in the region of a return bore between a control chamber of the fuel injector and a low-pressure region. In particular, the sensor surrounds the return bore at a sleeve-like section of a component in which the return bore is formed. An end portion of an injection member configured as a nozzle needle projects into the control chamber. The movement of the nozzle needle is controlled in known fashion by influencing the pressure in the control chamber to open spray holes formed in the injector housing in order to inject fuel into the combustion chamber of an internal combustion engine. The pressure in the control chamber is effected by drainage of fuel from said control chamber into the low-pressure region via the return bore or return throttle, it being possible to close the return bore by means of a closing member in the low-pressure region of the injector housing, which closing member can in turn be actuated by means of an actuator, for example a magnetic actuator or a piezo actuator. In the lowered position of the nozzle needle a relatively high (hydraulic) pressure is present in the control chamber and therefore also in the return bore. Upon depressurization of the control chamber, by contrast, fuel flows from the control chamber into the low-pressure region, the hydraulic pressure in the return bore being reduced. The known sensor is designed to detect the pressure or pressure fluctuations in the return bore caused by opening of the closing member leading from the control chamber, from which the position of the nozzle needle can be deduced. A disadvantage of the known arrangement is that the sensor is arranged in the high-pressure region of the injector housing and must therefore be of relatively high-cost construction. In addition, the installation space available for such a sensor in the injector housing is restricted, so that special design solutions, which are critical, in particular, with respect to the strength of the injector housing, must be selected. 
     A fuel injector having pressure sensing means arranged in the low-pressure region is known from DE 10 2011 051 765 A1. In this case a measuring duct or tap hole leads to a diaphragm-like intermediate wall. The pressure sensing means or force sensing element is arranged on the rear side of the intermediate wall. The pressure sensing means is preferably a measuring strip arrangement of low stiffness, which measures the tensions or deformations arising in the intermediate wall. However, because of the high pressures in the tap hole, problems relating to the strength of the intermediate wall can arise. 
     SUMMARY 
     In contrast of the above, the fuel injector according to the disclosure has increased durability in the region of the pressure sensing means because the pressure is not measured by means of a tension or deformation of the intermediate wall. According to the disclosure, the load is measured by a force sensing element as stiff as possible, which supports the intermediate wall, so that the intermediate wall is subjected to practically no deformation. 
     To this end, the fuel injector includes an injector housing in which a nozzle chamber is configured, which nozzle chamber can be supplied with pressurized fuel via a feed line formed in the injector housing. A longitudinally movable nozzle needle, which opens or closes at least one spray hole, is arranged in the nozzle chamber. The fuel injector further includes a force sensing element for at least indirectly detecting a pressure in a pressure chamber formed in the injector housing. The pressure chamber is hydraulically connectable to the feed line. The force sensing element is arranged in a measuring chamber configured in the injector housing, the measuring chamber being separated from the pressure chamber by a diaphragm-like intermediate wall. According to the disclosure, the force sensing element supports the intermediate wall. In addition, the force sensing element advantageously has very high stiffness. The intermediate wall is therefore reinforced by the support of the force sensing element against the direction of action of the pressure in the pressure chamber which is to be measured, so that the tensions and deflections in the intermediate wall when loaded by the pressure are minimized. 
     In an advantageous development, the force sensing element is preloaded against the intermediate wall. The high pressure prevailing in the pressure chamber during operation of the fuel injector then counteracts the preloading or deflection of the intermediate wall, so that the deformations and tensions—specifically the tensile loadings—in the intermediate wall and in the surrounding regions are minimized. On the high-pressure side of the intermediate wall the pressure variations are highly dynamic, so that preloading of the intermediate wall by the force sensing element results in a significant increase in durability. 
     In an advantageous embodiment, the force sensing element is preloaded by a screw element, for example a nut. The preloading of the force sensing element, and therefore of the intermediate wall, can thereby be very precisely adjusted during assembly of the fuel injector. 
     In another advantageous embodiment, the force sensing element is pretensioned by means of an overdimension inside the injector housing. The force sensing element has an overdimension in relation to the measuring chamber, so that the force sensing element is preloaded simultaneously with the axial clamping of the injector housing during assembly. This is an especially low-cost implementation of the preloading. 
     In a preferred embodiment of the force sensing element, the latter is configured as a piezoelectric force sensing element. Such an element has the advantage of relatively high measuring sensitivity combined with a compact structure and low manufacturing costs. Furthermore, such a force sensing element can be constructed especially stiff, thereby bracing the intermediate wall very effectively. 
     In an advantageous embodiment, the pressure chamber is connected hydraulically to the nozzle chamber via a connecting bore. The pressure progression within the nozzle chamber, and therefore the pressure with which the fuel is injected into the combustion chamber of the internal combustion engine, is thereby detected. In this case the connecting bore is advantageously formed in a throttle plate of the injector housing. 
     In a development of the disclosure, the longitudinal movement of the nozzle needle is controlled by the pressure in a control chamber. The pressure in the control chamber can in turn be controlled, for example, by a pilot valve. 
     In an advantageous configuration, the pressure chamber is connected hydraulically to the control chamber via a tap hole. The pressure in the control chamber is thereby detected, which pressure predominantly influences the movement of the hydraulically activated nozzle needle. In this case the tap hole is advantageously formed in the throttle plate of the injector housing, in which throttle plate a return throttle from the control chamber to the pilot valve is also formed. The pressure in the control chamber is subjected to larger fluctuations than the pressure in the nozzle chamber. Pressure differences in the control chamber can thereby be determined more reliably than pressure differences in the nozzle chamber. 
     In advantageous embodiments, a valve chamber is formed in the pilot valve and the control chamber is connected hydraulically to the valve chamber via a return throttle. The nozzle needle is thereby connected as a servo valve. The pilot valve may be configured, for example, as a directly connected solenoid valve. The pressure in the valve chamber is subjected to still larger fluctuations than the pressure in the control chamber. Consequently, the pressure differences can be determined very reliably in this embodiment also. 
     In an advantageous development, the pressure chamber is connected hydraulically to the valve chamber via a channel. The hydraulic connection from the valve chamber to the pressure chamber is thereby implemented in a very simple manner. In this case the pressure chamber and the channel are advantageously implemented as one volume, for example as a continuous channel, so that the connection between valve chamber and pressure chamber is especially inexpensive. 
     In another advantageous embodiment the feed line is connected to the pressure chamber. The pressure drop between nozzle chamber and a high-pressure source—that is, approximately the pressure drop of the nozzle chamber—is thereby measured. This embodiment can be implemented at especially low cost and has advantages with regard to the installation space required, since the measurement by the force sensing element may be effected, for example, remotely from the nozzle needle, that is, in a region in which more free installation space89* is present than in a region close to the nozzle. 
     In advantageous embodiments, the injector housing includes a nozzle body, a throttle plate, a valve plate and a retaining body which are braced together axially by means of a nozzle-clamping nut. This is a very advantageous structure of a fuel injector, especially of a fuel injector having a hydraulic pilot valve which, in turn, can be activated, for example, by an electromagnetic actuator. Fuel injectors of this type are operated by variation of hydraulic pressures. Detection of pressures and pressure differences is therefore of especially great advantage with such fuel injectors, firstly in order to determine the injection characteristic curve, but also, secondly, in order to obtain the desired injection characteristic curve robustly over the service life through specified evaluation of the pressure progressions. 
     In a development of the disclosure, the measuring chamber is formed in the valve plate, a pilot valve seat of the pilot valve being arranged on the valve plate in order to control the nozzle needle. The force sensing element and at least parts of the hydraulic pilot valve are thereby arranged in an installation-space saving manner in a component of the injector housing, namely in the valve plate. 
     In an alternative development, the measuring chamber is formed in the throttle plate, the throttle plate delimiting the nozzle chamber. This, too, is an installation-space saving arrangement of the force sensing element, since the throttle plate is already a component of the injector housing in any case. 
     The disclosure also includes the use of a fuel injector according to the disclosure in compression-ignition internal combustion engines. In this case the system pressure prevailing in the fuel injection system is preferably more than 2000 bar. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages, features and details of the disclosure are apparent from the following description of preferred exemplary embodiments, and from the drawings, in which: 
         FIG. 1  shows a longitudinal section through a fuel injector according to the disclosure with a force sensing element for detecting a pressure or for detecting pressure fluctuations, only the essential regions being represented, 
         FIG. 2  shows a section of a further exemplary embodiment of the fuel injector in longitudinal section, only the essential regions being represented, 
         FIG. 3  shows a section of another further exemplary embodiment of the fuel injector in longitudinal section, only the essential regions being represented, 
         FIG. 4  shows the bracing concept of the force sensing element inside the fuel injector. 
     
    
    
     DETAILED DESCRIPTION 
     Like elements or elements having the same function are provided in the Figures with the same reference numerals. 
       FIG. 1  shows a fuel injector  1  according to the disclosure serving as a component of a so-called common rail injection system for injecting fuel into the combustion chamber of an internal combustion engine (not shown). In particular, in this case the common rail injection system has a system pressure of more than 2000 bar. 
     The fuel injector  1  comprises a injector housing  10  which in the exemplary embodiment represented comprises essentially four components adjoining one another in the axial direction: on the side facing towards the combustion chamber (not shown) of the internal combustion engine the injector housing  10  has a nozzle body  10   a  adjoined by a throttle plate  10   b  which in turn is a adjoined on the side facing away from the nozzle body  10   a  by a valve plate  10   c  and a retaining body  10   d . These components of the injector housing  10  are braced together axially in a sealing manner by a nozzle clamping nut  10   e.    
     A blind hole  31  having at least one, but preferably a plurality of spray holes  9  for injecting the pressurized fuel into the combustion chamber of the internal combustion engine, is formed in the nozzle body  10   a . The nozzle body  10   a  forms in a bore-shaped recess a nozzle chamber  6  which is, connected hydraulically via a feed line  7  to a fuel source, for example a common rail. A reciprocatingly movable injection member in the form of a nozzle needle  2  is arranged inside the nozzle chamber  6 . 
     A nozzle seat  8  with which the nozzle needle  2  cooperates to open and close the spray holes  9  is arranged on the nozzle body  10   a.    
     The nozzle needle  2  is guided radially in the nozzle chamber  6  by the nozzle body  10   a , the nozzle needle  2  being loaded by a force in the direction of the nozzle seat  8  by a closing spring  35 . At its end facing away from the nozzle seat  8  the nozzle needle  2  delimits with an end face a control chamber  4 . The control chamber  4  is formed in the injector housing  10  between the nozzle needle  2 , the throttle plate  10   b  and a sleeve  36 . The control chamber  4  is connected to the feed line  7  by a feed throttle  11  formed in the throttle plate  10   b . The sleeve  36  is tensioned against the throttle plate  10   b  by the closing spring  35  and guides the nozzle needle  2  in a longitudinally movable manner, while the nozzle needle  2  positions the sleeve  36  in the radial direction. The pressure in the control chamber  4  loads the nozzle needle  2  with a hydraulic force in the direction of the nozzle seat  8 , that is, in the closing direction. 
     The pressure in the control chamber  4  is controlled by a pilot valve  3  arranged in the injector housing  10 . The pilot valve  3  comprises a closing body  40 , which cooperates with a pilot valve seat  21  configured on the valve plate  10   c , an actuator  41  and a valve chamber  20 . In the exemplary embodiment in  FIG. 1  the actuator  41  is shown as an electromagnetic actuator, but may also be any kind of actuator, for example, a piezo actuator. The valve chamber  20  is connected to the control chamber  4  via a return throttle  5  formed in the throttle plate  10   b . By interacting with the pilot valve seat  21 , the closing body  40  opens and closes a connection between the valve chamber  20  and a low-pressure chamber  42  configured in the injector housing  10 . In the exemplary embodiment of  FIG. 1  the valve chamber  20  includes essentially two bores, formed respectively in the valve plate  10   c  and in the throttle plate  10   b . In alternative embodiments, however, the valve chamber  20  may have any desired form. 
     According to the disclosure, a force sensing element  17  is arranged in the injector housing  10  in order to measure a pressure in a pressure chamber  14  subjected to high pressure. Two electrical conduits  17   a  lead from the force sensing element  17  through the injector housing  10  to a control device (not shown). The stroke movement of the nozzle needle  2 , and therefore the injection characteristic curve of the fuel injector  1 , can be derived directly from the force or pressure measurement. The activation of the pilot valve  3  can then, for example, be varied by the control device as a function of the injection characteristic curve. 
     The pressure chamber  14  is connected hydraulically to the feed line  7 , to the nozzle chamber  6 , to the control chamber  4  or to the valve chamber  20 . In the exemplary embodiment of  FIG. 1  the pressure chamber  14  is formed by a recess in the valve plate  10   c  and is connected to the control chamber  4  via a tap hole  12  formed in the throttle plate  10   b.    
     Furthermore, a measuring chamber  16  is formed in the valve plate  10   c  opposite the pressure chamber  14 , from which it is separated by a diaphragm-like intermediate wall  13 . The force sensing element.  17  is arranged in the measuring chamber  16 , and specifically in such a way that it supports the intermediate wall  13 . 
     The measuring chamber  16  is the form of a blind hole open towards the retaining body  10   d . The force sensing element  17  can thereby be braced against the intermediate wall  13  either by means of an overdimension with respect to the retaining body  10   d  or, as in the exemplary embodiment of  FIG. 1 , by means of a screw element  18  screwed into the measuring chamber  16 . 
     The measuring chamber  16  is located in the low-pressure region, while the pressure chamber  14  is subjected to high pressure. This has the result that the intermediate wall  13  is loaded hydraulically on one side. The preloading of the intermediate wall  13  by the force sensing element  17  compensates for this one-sided loading. The maximum stresses, in particular tensile stresses, in the intermediate wall  13  are thereby reduced and the service life of the entire fuel injector  1  is therefore increased. 
     Further embodiments of the fuel injector  1  according to the disclosure are described below. Regions not described in detail are implemented as in the exemplary embodiment of  FIG. 1 . 
       FIG. 2  shows the force sensing element  17  in an alternative arrangement, specifically with regard to the measurement of pressure in the valve chamber  20 . Analogously to the embodiment in  FIG. 1 , the measuring chamber  16  is in the form or a blind hole in the valve plate  10   c , the blind hole being open towards the retaining body  10   d . The force sensing element  17  has, in the longitudinal direction of the fuel injector  1 , an overdimension in relation to the measuring chamber  16 . During assembly of the fuel injector  1 , the force sensing element  17  is thereby preloaded between the retaining body  10   d  and the intermediate wall  13 , as the nozzle clamping nut  10   e  is tightened. 
     On the side of the intermediate wall  13  opposite the measuring chamber  16 , the pressure chamber  14  is formed as a recess in the valve plate  10   c  and is delimited by the valve plate  10   c  and the throttle plate  10   b . The pressure chamber  14  is connected to the valve chamber  20  via a channel  15  also formed in the valve plate  10   c , so that the pressure prevailing in the valve chamber  20  is also present in the pressure chamber  14 . 
     In alternative embodiments the pressure chamber  14  and the channel  15  may also be implemented as a single recess. Furthermore, the pressure chamber  14  and/or the channel  15  may also be formed in the throttle plate  10   b.    
       FIG. 3  shows the force sensing element  17  in a further arrangement, specifically with regard to measuring the pressure in the nozzle chamber  6 . Analogously to the exemplary embodiment of  FIG. 2 , here the force sensing element  17  is braced in the measuring chamber  16  by means of an overdimension between the retaining body  10   d  and the intermediate wall  13 . A connecting bore  32  is formed in the throttle plate  10   b  and connects the nozzle chamber  6  to the pressure chamber  14 , so that the pressure prevailing in the nozzle chamber  6  is also present in the pressure chamber  14 . The pressure chamber  14  is configured as a recess or blind hole in the valve plate  10   c , but may also be formed in the throttle plate  10   b  in alternative embodiments. 
       FIG. 4  shows a concept according to the disclosure for bracing the force sensing element  17  in the measuring chamber  16 . The force sensing element  17  is provided with an overdimension  19  with respect to the measuring chamber  16  ( FIG. 4 , top). If the force sensing element  17  is now braced between the retaining body  10   d  and the intermediate wall  13 , a deflection of the diaphragm-like intermediate wall  13  in the direction of the pressure chamber  14  is produced ( FIG. 4 , bottom). The high pressure occurring in the pressure chamber  14  during operation then counteracts the deflection of the intermediate wall  13 , so that the tensile stresses in the intermediate wall  13  and in the surrounding regions are minimized during operation of the fuel injector  1 . 
     Alternatively, it is also possible to implement the bracing of the force sensing element  17  in the measuring chamber  13  by means of a screw connection, as shown in the embodiment of  FIG. 1 . 
     Furthermore, it is also alternatively possible to form the measuring chamber  16  in the throttle plate  10   b , so that the force sensing element  17  is arranged within the throttle plate  10   b . The force sensing element  17  can then be braced between the throttle plate  10   b  and the valve plate  10   c , or between the throttle plate  10   b  and the retaining body  10   d , in the event that the measuring chamber  16  is formed, for example, as a through-bore in the valve plate  10   c.    
     The operation of the fuel injector  1  according to the disclosure is as follows: 
     The opening and closing of the nozzle needle  2  of the fuel injector  1  is controlled by means of the pilot valve  3 . When the pilot valve  3  is activated and opened by the actuator  41 , so that the closing body  40  is lifted from the pilot valve seat  21 , the valve chamber  20  is connected to the low-pressure chamber  42 . The pressure above the nozzle needle  2  in the control chamber  4  is thereby lowered via the return throttle  5  and the pilot valve seat  21 . In this way the nozzle needle  2  is moved upwards from the nozzle seat  8  by the pressure in the nozzle chamber  6  which remains equal to the system pressure, and the injection quantity reaches the combustion chamber of the internal combustion engine via the feed line  7 , the nozzle chamber  6 , the nozzle seat  8 , the blind hole  31  and the spray holes  9 . 
     When the pilot valve  3  is closed again the pressure in the control chamber  4  builds up again via the feed throttle  11 , the nozzle needle  2  is again pressed downwards against the nozzle seat  8 , and the injection is ended. 
     During this cycle the pressure in the control chamber  4  has a characteristic progression: with the pilot valve  3  unactuated, that is, closed, the pressure in the control chamber  4  corresponds to the pressure in the nozzle chamber  6 , which corresponds to the system pressure. When the pilot valve  3  opens, the pressure in the control chamber  4  drops, since more fuel flows out of the control chamber  4  through the return throttle  5  than flows in through the feed throttle  11 . Thereupon the nozzle needle  2  moves in the opening direction, that is, away from the nozzle seat  8 . As long as the nozzle needle  2  is in motion, the pressure in the control chamber  4  results from the balance of forces acting on the nozzle needle  2 . That is, the pressure increases in the control chamber  4  because of the rising pressure in the blind hole  31  and the resulting upward force acting on the nozzle needle  2 , that is, away from the nozzle seat  8 . When the nozzle needle  2  has reached its maximum stroke and rests against the upper stroke stop, a drop in the pressure in the control chamber  4  occurs in accordance with the through-flows through the return throttle  5  and the feed throttle  11 . 
     When the pilot valve  3  is closed again, the pressure in the control chamber  4  rises until an equilibrium of the forces acting on the nozzle needle  2  is established and the nozzle needle  2  again moves in the direction of the nozzle seat  8 . When the nozzle needle  2  contacts the nozzle seat  8 , the pressure in the control chamber  4  finally rises again to the system pressure. These relationships between the pressure in the control chamber  4  and the strokes of pilot valve  3  and nozzle needle  2  also apply in ballistic operation of the nozzle needle  2 , that is, when the injection duration is so short that the nozzle needle  2  does not reach the stroke stop. 
     The pressure in the control chamber  4  may be transmitted onwards, for example via the tap hole  12 , to a suitable location for the pressure chamber  14 . Advantageously, the pressure chamber  14  is located in the region of a flat sealing face inside the injector housing  10 . 
     The pressure in the valve chamber  20  between the return throttle  5  and the pilot valve seat  21  also behaves in a similar manner to the pressure in the control chamber  4 . That is to say that the pressure in the valve chamber  20  can also be used for assessing the movement of the pilot valve  3  and/or of the nozzle needle  2 . The pressure in the valve chamber  20  may be conducted, for example, via the channel  15  to the pressure chamber  14 . 
     Furthermore, the pressure in the nozzle chamber  6  may also be measured and used for assessing the movement of the nozzle needle  2 . For example, the pressure in the nozzle chamber  6  may be conducted for this purpose through the connecting bore  32  to the pressure chamber  14 . 
     The diaphragm-like intermediate wall  13  may be implemented in the form of the base of the blind hole or of the measuring chamber  16  in the valve plate  10   c  or in the throttle plate  10   b . The force sensing element  17 , which is very stiff in the longitudinal direction and which indirectly detects the pressure or the pressure fluctuations in the pressure chamber  14 , is inserted in the measuring chamber  16 . A strong support against deflection of the intermediate wall  13  is predominantly provided by the force sensing element  17 . The force sensing element  17  may be, for example, a piezo force transducer which is braced against the intermediate wall  13  by the screw element  18  or by an overdimension. The diaphragm-like intermediate wall  13  is loaded by the preloading against the direction or action of the pressure to be measured in the pressure chamber  14 , so that the stresses arising in the intermediate wall  13  as a result of pressure loading are minimized during operation of the fuel injector  1 .