Patent Publication Number: US-6659086-B2

Title: Fuel injection apparatus for internal combustion engines

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is directed to an improved fuel injection apparatus for internal combustion engines having a fuel pump for each engine cylinder. 
     2. Description of the Prior Art 
     One fuel injection apparatus of the type with which this invention is concerned is known from the literature, for instance from the textbook entitled  Dieselmotor - Management  [Diesel Engine Management], 2nd Ed., Verlag Vieweg, page 299. This known fuel injection apparatus, for each cylinder of the engine, has one fuel pump, one fuel injection valve, and one line connecting the fuel injection valve to the fuel pump. The fuel pump has a pump piston, driven in a reciprocating motion, that defines a pump work chamber. Near the fuel pump is a control valve, by which a communication of the pump work chamber with a relief chamber is controlled. The fuel injection valve has an injection valve member, by which at least one injection opening is controlled and which is movable in the opening direction counter to a closing force by means of the pressure generated in the pump work chamber by the fuel pump. By means of the control valve, the instant and duration of opening of the fuel injection valve can be controlled; the instant of opening is determined by providing that the pump work chamber is disconnected from the relief chamber by the control valve, and thus the high pressure generated by the fuel pump in the pump work chamber is operative. For closure of the fuel injection valve, the pump work chamber of the fuel pump is made to communicate with the relief chamber by the control valve, so that no further high pressure is operative in the pump work chamber, and the fuel injection valve is closed by the closing force acting on the injection valve member. The control valve is-disconnected by means of the line and is located relatively far from the fuel injection valve, so that when the communication of the pump work chamber with the relief chamber is opened by the control valve, the pressure at the fuel injection valve drops only in delayed fashion, and accordingly the fuel injection valve closes only with a delay, so that the instant and duration of opening of the fuel injection valve can be determined only imprecisely. A brief opening and closure of the fuel injection valve for a preinjection and postinjection that are chronologically offset from a main injection is thus feasible only with difficulty. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The fuel injection apparatus of the invention has the advantage over the prior art that by means of a second control valve, a fast, undelayed closure of the fuel injection valve is made possible, as is necessary in particular to make a preinjection and postinjection that are chronologically offset from a main injection possible. To close the fuel injection valve, a high pressure is established by the second control valve in the pressure chamber of the fuel injection valve, and by this pressure the injection valve member is urged in the closing direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings. 
     FIG. 1 shows a fuel injection apparatus for an internal combustion engine schematically in a first exemplary embodiment; 
     FIG. 2 shows a pressure course at injection openings of a fuel injection valve of the fuel injection apparatus in the first exemplary embodiment; 
     FIG. 3 shows a course of a pressure at injection openings of a fuel injection valve of the fuel injection apparatus; 
     FIG. 4 is a detail of a modified version of the fuel injection apparatus in the second exemplary embodiment; 
     FIG. 5 shows the fuel injection apparatus in a third exemplary embodiment; and 
     FIG. 6 shows the fuel injection apparatus in a fourth exemplary embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIGS. 1,  3 ,  5  and  6 , a fuel injection apparatus for an internal combustion engine of a motor vehicle is shown. The fuel injection apparatus is preferably embodied as a so-called pump-line-nozzle system and for each cylinder of the engine has one fuel pump  10 , one fuel injection valve  12 , and one line  14  connecting the fuel injection valve  12  to the fuel pump  10 . The fuel pump  10  has a pump piston  18 , guided tightly in a cylinder  16  and driven in a reciprocating motion by a cam  20  of a camshaft of the engine. In the cylinder  16 , the pump piston  18  defines a pump work chamber  22 , in which fuel is compressed at high pressure by the pump piston  18 . By means of a low-pressure pump, not shown, for instance, fuel from a fuel tank  24  is delivered to the pump work chamber  22 . 
     The fuel injection valve  12  is disposed separately from the fuel pump  10  and communicates with the pump work chamber  22  via the line  14 . The fuel injection valve  12  has a valve body  26 , which may be embodied in multiple parts and in which a piston-like injection valve member  28  is guided longitudinally displaceably in a bore  30 . The valve body  26 , in its end region oriented toward the combustion chamber of the cylinder of the engine, has at least one and preferably a plurality of injection openings  32 . The injection valve member  28 , in its end region toward the combustion chamber, has a sealing face  34 , which for instance is approximately conical, and which cooperates with a valve seat  36 , embodied in the valve body  26  in its end region toward the combustion chamber; the injection openings  32  lead away from or downstream of this valve seat. In the valve body  26 , between the injection valve member  28  and the bore  30 , toward the valve seat  36 , there is an annular chamber  38 , which as a result of a radial widening of the bore  30  changes over into a pressure chamber  40  surrounding the injection valve member  28 . The injection valve member  28  has a pressure shoulder  42  In the region of the pressure chamber  40 . The end remote from the combustion chamber of the injection valve member  28  is engaged by a prestressed closing spring  44 , by which the injection valve member  28  is pressed toward the valve seat  36 . The closing spring  44  is disposed in a spring chamber  46  of the valve body  26  that adjoins the bore  30 . The spring chamber  46  is adjoined, on its end remote from the bore  30 , in the valve body  26  by a further bore  48 , in which a piston  50  that is joined to the injection valve member  28  is tightly guided. The piston  50 , with its end face remote from the injection valve member  28 , defines a control pressure chamber  52  in the valve body  26 . Embodied in the valve body  26  is a conduit  54 , into which the line  14  to the fuel pump  10  discharges and which itself discharges into the pressure chamber  40 , and from which a communication  56  branches off to the control pressure chamber  52 . 
     The fuel injection apparatus has a first control valve  60 , disposed near the fuel pump  10 , that can for instance be integrated with the fuel pump  10 . By means of the first control valve  60 , a communication  59  of the pump work chamber  22  with a relief chamber  24  is controlled; the relief chamber is for instance the fuel tank  24 , or some other region in which a low pressure prevails. The first control valve  60  is electrically triggerable and has an actuator  61 , which can be an electromagnet or a piezoelectric actuator and is electrically triggered and by which a valve member of the control valve  60  is movable. The first control valve  60  can be embodied as either pressure-balanced or not. 
     In a first exemplary embodiment of the fuel injection apparatus, shown in FIG. 1, the first control valve  60  is embodied as a 2/2-way valve. In a first switching position of the control valve  60 , the communication  59  of the pump work chamber  22  of the fuel pump  10  with the relief chamber  24  is opened by this valve, so that a high pressure cannot build up in the pump work chamber  22 . In a second switching position, by means of the control valve  60  the communication  59  of the pump work chamber  22  with the relief chamber  24  is broken, so that in the pump work chamber  22 , in the pumping stroke of the pump piston  18 , high pressure can build up. The fuel injection apparatus furthermore has a second control valve  64 , disposed near the fuel injection valve  12 , by means of which control valve a communication  63  of the control pressure chamber  52  of the fuel injection valve  12  with a relief chamber is controlled; the relief chamber is the fuel tank  24  or some other region where a low pressure prevails. The control valve  64  is electrically controllable and has an actuator  65 , which may be an electromagnet or a piezoelectric actuator, and which is electrically triggered and by which a valve member of the control valve  64  is movable. The second control valve  64  is embodied as a 2/2-way valve; in a first switching position, the communication  63  of the control pressure chamber  52  with the relief chamber  24  is opened by the control valve  64 , and in a second switching position the communication  63  of the control pressure chamber  52  with the relief chamber  24  is broken. The second control valve  64  is preferably embodied in pressure-balanced form. A throttle restriction  57  is disposed in the communication  56  of the control pressure chamber  52  with the conduit  54 . A throttle restriction  58  is also disposed in the communication  63  of the control pressure chamber  52  with the relief chamber  24 . The first control valve  60 , in the untriggered or in other words currentless state, is in a switching position in which the communication  59  of the pump work chamber  22  with the relief chamber  24  is open. The second control valve  64 , in the nontriggered or in other words currentless state, is in its switching position in which the communication  63  of the control pressure chamber  52  with the relief chamber  24  is open. 
     The function of the fuel injection apparatus in the first exemplary embodiment will now be explained. The control valves  60 ,  64  are triggered by an electric control unit  68 . In the intake stroke of the pump piston  18 , the first control valve  60  is opened, so that the pump work chamber  22  communicates with the relief chamber  24 . When the injection is to begin, the first control valve  60  is closed by suitable triggering by the control unit  68 , so that the pump work chamber  22  is disconnected from the relief chamber  24 , and a high pressure builds up in it. The pressure prevailing in the pump work chamber  22  is also operative in the pressure chamber  40 , via the line  14  and the conduit  54  in the valve body  26 . The second control valve  64  is kept open by the control unit  68 , so that a high pressure cannot build up in the control pressure chamber  52  and instead this pressure is relieved to the relief chamber  24 . By means of the throttle restrictions  57 ,  58 , it is attained that only a slight quantity of fuel can flow out of the conduit  54  into the relief chamber  24 . By means of the high pressure acting in the pressure chamber  40  on the pressure shoulder  42  of the injection valve member  28 , the injection valve member  28  is moved in the opening direction  29  counter to the force of the closing spring  44 , so that the injection valve member uncovers the injection openings  42 , and fuel is injected into the combustion chamber of the cylinder. 
     After that, the first control valve  60  is closed again by the control unit  68 , so that fuel can flow out of the pump work chamber  22  into the relief chamber  24 , and the high pressure is relieved. Accordingly, the pressure in the pressure chamber  40  of the fuel injection valve  12  drops as well, so that by the force of the closing spring  44 , the injection valve member  28  is moved with its sealing face  34  into contact with the valve seat  36  and closes the injection openings  32 , thus interrupting the injection. Because of the profile of the cam  20  that brings about the reciprocating motion of the pump piston  18 , only a relatively slight pressure builds up in the pump work chamber  22  and thus in the pressure chamber  40  of the fuel injection valve  12  during the first injection phase, which is a preinjection, and thus the preinjection occurs at a correspondingly low pressure and in an only slight quantity. In FIG. 2, the course of the pressure P at the injection openings  32  of the fuel injection valve  12  is shown over the time t during one complete injection cycle. The phase I represents the preinjection. 
     Next, the first control valve  60  is closed again by the control unit  68 , so that high pressure builds up in the pump work chamber  22  and in the pressure chamber  40  of the fuel injection valve  12 , as a function of the profile of the cam  20 . By means of the high pressure, the fuel injection valve  12  is opened again, and a fuel injection through the injection openings  32  into the combustion chamber of the cylinder ensues, with a main injection at a higher injection pressure and in a greater injection quantity than in the preceding preinjection. The course of the pressure at the injection openings  32  during the main injection is shown as phase II in FIG.  2 . 
     The second control valve  64  can remain open during the preinjection and during the main injection, so that the control pressure chamber  52  is in communication with the relief chamber  24 . It can also be provided that the second control valve  64  is closed after the preinjection, so that no further fuel can flow out of the control pressure chamber  52  into the relief chamber  24 , and the same pressure as in the pump work chamber  22  and in the pressure chamber  40  builds up in the control pressure chamber  52  as well. If for the main-injection the first control valve  60  is closed again, then the second control valve  64  can still be kept closed, so that in the control pressure chamber  52 , the same high pressure as in the pump work chamber  22  and in the pressure chamber  40  builds up. By means of the high pressure in the control pressure chamber  52 , a force acting in the closing direction, that is, counter to the opening direction  29 , acting on the piston  50  and thus on the injection valve member  28  is generated, so that the injection valve member  28  is kept with its sealing face  34  in contact with the valve seat  36  and closes the injection openings  32 , so that no injection occurs. The pressure in the pump work chamber  22  and in the pressure chamber  40  builds up in accordance with the profile of the cam  20 . Not until the second control valve  64  is opened and thus the high pressure in the control pressure chamber  52  is relieved to the relief chamber  24  can the fuel injection valve  12  open, as a result of the movement of the injection valve member  28  in the opening direction  29  by the high pressure prevailing in the pressure chamber  40 , counter to the force of the closing spring  44 . Thus because of the delayed opening of the second control valve  64 , the opening pressure of the fuel injection valve  12  can be raised, as is represented by dashed lines in FIG. 2 for the main injection phase II. 
     For terminating the main injection, the second control valve  64  is closed, so that the control pressure chamber  52  is disconnected from the relief chamber  24 , and the high pressure of the pump work chamber  22  builds up in it. By the high pressure in the control pressure chamber  52 , the fuel injection valve  12  is closed and the fuel injection is interrupted. The first control valve  60  can either remain closed or be open. For a postinjection of fuel, the second control valve  64  is opened again, so that the control pressure chamber  52  is relieved, and the fuel injection valve  12  is opened again by the high pressure still prevailing in the pump work chamber  22  and in the pressure chamber  40 . The postinjection is shown in FIG. 2 as injection phase III. The postinjection takes place at high pressure, which is generated by the corresponding profile of the cam  20 . The first control valve  60  is closed during the postinjection. To terminate the fuel injection, the first control valve  60  is opened, so that the pump work chamber  22  is relieved, and the fuel injection valve  12  closes by the force of the closing spring  44 . The second control valve  64  can be in either its closed or open position then. 
     In FIG. 3, the fuel injection apparatus is shown in a second exemplary embodiment, in which the layout is essentially the same as in the first exemplary embodiment and only the first control valve  160  is modified. The first control valve  160  has an electrically triggerable actuator  161 , in the form of an electromagnet or a piezoelectric actuator, by which a valve member of the control valve  160  is movable. The control valve  160  is embodied as a 2/3-way-valve and can accordingly assume three switching positions. In a first switching position, the communication  59  of the pump work chamber  22  with the relief chamber  24  is fully opened by the control valve  160 . In a second switching position, the communication  59  of the pump work chamber  22  with the relief chamber  24  is opened by the control valve  160  via a throttled passage, and in a third switching position the communication  59  of the pump work chamber  22  with the relief chamber  24  is broken by the control valve  160 . The second switching position of the control valve  160  can be achieved by providing that its valve member, as a result of the actuator  161 , executes only a partial stroke and thus opens only a smaller flow cross section than in the first switching position. The triggering of the first control valve  160  by the control unit  68  is in principle the same as is described above for the first exemplary embodiment; at the onset of the main injection, the control valve  160  is moved into its second switching position, in which the pump work chamber  22  has a throttled communication with the relief chamber  24 . By means of this throttled communication, it is attained that some of the fuel pumped by the pump piston  18  flows out into the relief chamber  24 , and as a result the pressure in the pump work chamber  22  reaches only a lesser height than when the control valve  160  is fully closed. As a result, it is attained that at the onset of the main injection, the fuel injection takes place at only a relatively slight pressure, as is illustrated in FIG. 4, which again shows the course of the pressure at the injection openings  32  of the fuel injection valve  12 . At a certain instant, the control unit  68  moves the first control valve  160  into its third switching position, in which the pump work chamber  22  is disconnected from the relief chamber  24 , and the full high pressure corresponding to the profile of the cam  20  is established in the pump work chamber  22  and thus at the injection openings  32  of the fuel injection valve  12 . The instant of the full pressure rise in the pump work chamber  22  is determined by the instant of closure of the first control valve  160 . 
     Otherwise, the triggering of the first control valve  160  and of the second control valve  64  by the control unit  68  is the same as has been described for the first exemplary embodiment, and thus the pressure course at the injection openings  32  shown in FIG. 4 results, with the preinjection phase I, the main injection phase II with a graduated pressure buildup, and the postinjection phase III. By a delayed opening of the second control valve  64 , the opening pressure of the fuel injection valve  12  can again be increased, as is represented in FIG. 4 by the dashed line showing the course of the main injection phase II. 
     In FIG. 5, the fuel injection apparatus in a third exemplary embodiment is shown, in which the basic layout is as in the first or second exemplary embodiment, and only the second control valve  164  has been modified. The second control valve  164  is embodied as a 2/2-way valve, but in a departure from the first and second exemplary embodiments, in the nontriggered or in other words currentless state of its actuator  165 , this control valve is in a switching position in which the communication  63  of the control pressure chamber  52  with the relief chamber  24  is broken. This is advantageous for safety reasons, in order to assure that in the event of an interruption in the electrical connection between the second control valve  164  and the control unit  68  to assure that the fuel injection valve  12  cannot open in response to the high pressure then building up in the control pressure chamber  52 . 
     In FIG. 6, the fuel injection apparatus is shown in a fourth exemplary embodiment, in which the basic layout is again the same as in the exemplary embodiments explained above, and only the disposition of the second control valve  264  is modified. The second control valve  264  is disposed in the communication  56  of the control pressure chamber  52  with the conduit  54  and is embodied as a 2/2-way valve. A throttle restriction  58  is disposed in the communication  63  of the control pressure chamber  52  with the relief chamber  24 . By means of the second control valve  264 , the communication  56  of the control pressure chamber  52  with the conduit  54  and thus with the pump work chamber  22  of the fuel pump  10  is controlled. The first control valve  160  can be a 2/2-way valve, or as shown in FIG. 6, it may a 2/3-way valve. 
     The function of the fuel injection apparatus in the fourth exemplary embodiment, to attain a pressure course of the kind shown in FIG. 4, will now be explained. For a preinjection in accordance with phase I of the pressure course in FIG. 4, the first control valve  160  is closed by the control unit  68 , so that the pump work chamber  22  is disconnected from the relief chamber  24 , and high pressure builds up in the pump work chamber  22 . The second control valve  264  is likewise closed, so that the control pressure chamber  52  is disconnected from the conduit  54  and thus from the pump work chamber  22  and is relieved to the relief chamber  24  via the communication  63 . Because of the high pressure operative in the pressure chamber  40  of the fuel injection valve  12 , the fuel injection valve  12  opens because its injection valve member  28  is moved in the opening direction  29 , counter to the force of the closing spring  44 . To terminate the preinjection, the first control valve  160  is opened, so that the pump work chamber  22  communicates with the relief chamber  24 ; as a result, the pressure in the pump work chamber  22  and in the pressure chamber  40  drops such that the fuel injection valve  12  closes in response to the force of the closing spring  44 , which exceeds the pressure force exerted on the injection valve member  28 . In addition, the second control valve  264  can also be opened, so that the control pressure chamber  52  communicates with the conduit  54  and thus with the pump work chamber  22 . 
     For the main injection in accordance with phase II of the pressure course in FIG. 4, the first control valve  160  is moved by the control unit  68  into its second switching position, in which the pump work chamber  22  has the throttled communication with the relief chamber  24 , so that only a reduced pressure can build up in the pump work chamber  22 . The second control valve  264  is closed, and thus the control pressure chamber  52  is relieved to the relief chamber  24 . As a result of the pressure prevailing in the pressure chamber  40 , the fuel injection valve  12  opens, and a fuel injection at slight pressure ensues. Next, the first control valve  160  is put into its closed switching position by the control unit  68 , so that the full high pressure corresponding to the profile of the cam  20  builds up in the pump work chamber  22 . A fuel injection through the fuel injection valve  12  now takes place at high pressure. 
     To terminate the main injection, the second control valve  264  is opened by the control unit  68 , so that the high pressure of the pump work chamber  22  is operative in the control pressure chamber  52 , which reinforces the force of the closing spring  44  via the piston  50 , so that the injection valve member  28  is moved in the closing direction and closes the fuel injection valve  12 . For a postinjection in accordance with phase III in FIG. 4, the second control valve  264  is closed again by the control unit  68 , so that the control pressure chamber  52  is relieved to the relief chamber  24 , and because of the high pressure prevailing in the pressure chamber  40  the injection valve member  28  is moved in the opening direction  29  and opens the fuel injection valve  12 . The postinjection is effected at high pressure and is terminated by providing that the first control valve  160  is opened by the control unit  68 , so that the pressure in the pump work chamber  22  is relieved to the relief chamber  24 . In addition, the second control valve  264  can also be opened by the control unit  68 , thus reinforcing the closure of the fuel injection valve  12 . 
     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.