Fuel injection valve for internal combustion engines

0001Fuel injection valve for internal combustion engines

0002State of the art

0003To reduce emissions and to increase the efficiency of internal combustion engines with direct fuel injection, it is an objective to inject the fuel atomized as finely as possible into the combustion chamber of the internal combustion engine. For this purpose, on the one hand, the injection pressure with which the fuel is injected through the fuel injection valve is increased. On the other hand, the number of injection holes of the fuel injection valve is increased, so that the diameter of the individual injection holes can be reduced. The aim of this measure is to increase the beam energy in injection jets while reducing the droplet diameter. If very small quantities are to be pumped, the injection times become very short at high pressures at the fuel injection valve.

0004European patent application EP 0 470 348 A1, for example, discloses a fuel injection valve with a variable injection cross section, in which two rows of injection openings are formed. These injection openings are controlled by an inner valve needle and a sleeve surrounding the valve needle, wherein both the sleeve and the inner needle are acted upon by closing springs which press them against a valve seat, whereby the injection openings are closed. If fuel is introduced under high pressure in corresponding pressure chambers, the sleeve and the inner needle are acted upon by the fuel pressure in these pressure chambers. Depending on the pressure of the introduced fuel only the inner needle lifts from the valve seat and releases the first row of injection ports or successively lift the inner needle and sleeve away from the valve seat so that both rows of injection ports are sequentially opened. The opening of the inner needle or the sleeve is thus pressure-controlled, so that the successive control of inner needle and outer sleeve is achieved by a clever design of the pressure surfaces and the force of the closing springs.

0005In addition, from the prior art stroke-controlled fuel injection systems are known in which a valve needle has a pressure surface which is constantly acted upon by fuel under high pressure in the opening direction. The counterforce is not generated by a closing spring, but hydraulically by a valve piston which acts on the valve needle and in turn by the fuel pressure in a control chamber exerts a closing force on the valve needle. As an example, the document DE 198 27 267 AI called here. By changing the fuel pressure in the control chamber, the closing force on the valve needle changes, so that it is moved by the hydraulic force on the pressure surface. Such stroke-controlled fuel injection systems are used in many modern internal combustion engines, in particular for self-igniting internal combustion engines in passenger cars. A combination of both systems, ie the variable injection cross-section and the stroke-controlled injection system, would be particularly advantageous for a further optimization of the combustion process. So far, however, this was not possible without great effort to transfer the variable injection cross section readily on the stroke-controlled systems. For this purpose, complicated sealing edges or additional control valves are needed, which are expensive to manufacture and expensive. to easily transfer the variable injection cross section to the stroke controlled systems. For this purpose, complicated sealing edges or additional control valves are needed, which are expensive to manufacture and expensive. to easily transfer the variable injection cross section to the stroke controlled systems. For this purpose, complicated sealing edges or additional control valves are needed, which are expensive to manufacture and expensive.

0006Advantages of the invention

0007The fuel injection valve according to the invention with the characterizing features of claim 1 has the advantage that with a stroke-controlled injection system, two rows of injection ports are successively aufsteuerbar and so a Einspritzverlaufsformung is possible without additional control edges or control valves are needed. In the outer valve needle, an inner valve needle is guided, wherein both the outer valve needle and the inner valve needle controls at least one injection port. In the fuel injection valve, a fuel-filled control chamber is formed, by the pressure of the valve needles are acted upon at least indirectly in the direction of the valve seat. If the pressure in the control room is changed, the closing force through the valve pins also changes,

0008In an advantageous embodiment of the invention, a throttle connection is formed by the opening stroke of the outer valve needle, so that the inner valve needle is no longer acted upon by the pressure in the control chamber. As a result, the closing force is reduced to the inner valve needle in a simple manner, without a control edge or another valve would be necessary.

0009In an advantageous embodiment, the outer valve needle is connected to an outer piston rod, whose end face is acted upon by the pressure in the control chamber and thereby generates the closing force on the valve member. As a result, the function of the valve needle and the pressurized piston rod can be separated from each other in an advantageous manner and thus optimally designed.

0010In a further advantageous embodiment, the throttle connection between the end face of the piston rod and a stationary base is formed, so that in a simple and thus easy to manufacture manner, the throttle connection can be formed.

0011In a further advantageous embodiment, the inner valve needle is also connected to an inner piston rod whose front side is also acted upon by the pressure in the pressure chamber and thus generates the closing force on the inner valve needle. As a result, the function of valve needle and piston rod can be separated here as well.

0012In a further advantageous embodiment, the inner piston rod is guided in the outer piston rod, so that both piston rods are arranged coaxially with each other. As a result, the connection of the outer piston rod to the outer valve needle and the inner valve needle to the inner piston rod can be realized in an advantageous manner in an advantageous manner.

0013In a further advantageous embodiment, during the opening stroke movement of the inner valve needle, the inner piston rod comes into abutment against a stop surface formed on the inner side of the outer piston rod. As a result, the stroke stop of the inner valve needle is realized in a simple manner, without a stroke stop must be formed on the housing of the fuel injection valve.

0014In a further advantageous embodiment, the outer piston rod has an inwardly cantilevered region at its end facing away from the combustion chamber. As a result, an inner control chamber is bounded by the outer valve needle, the inwardly cantilevered region and the inner valve needle, which is connected to the control chamber, wherein the connection is in the form of a connecting bore. As a result, the pressure equalization between the control chamber and the inner control chamber and thus the closing force on the inner valve needle in the opening stroke can be tuned by design of the connecting hole, so that a defined successive opening of the outer valve needle and inner valve needle takes place and thus the desired Einspritzverlaufsfor- tion.

0015In a further advantageous embodiment of the invention, the inner valve needle on a pressure surface which is acted upon by the pressure in the pressure chamber only after the outer valve needle has lifted from the valve seat. This results in an opening force on the inner valve needle only if an injection is to take place. As a result, no opening force acts on the inner valve needle between the injections and the latter always closes the injection openings assigned to it safely.

0016In a further advantageous embodiment of the invention, the pressure in the control chamber is adjusted by a controllable by a valve connection with a leakage oil chamber. So only this one 2/2 valve is necessary for the pressure control, since the inlet throttle remains unchanged. In a further advantageous embodiment of the invention closes the outer piston rod at the opening stroke of the outer valve needle, the inlet throttle at least partially. This results in a further reduction of the pressure in the control chamber, so that the closing force on the inner valve needle decreases further. By an appropriate design of the opening forces on the valve needles can be achieved that the inner valve needle only after the outer valve needle has closed the inlet throttle, performs a Öffnungshubbewegung and so the injection ports are opened successively. In this way, the injection rate at the beginning of the injection is smaller than during the main injection, in which all the injection openings are released, so that a Einspritzverlaufsformung is achieved.

0017Further advantages and advantageous embodiments of the subject invention are the description of the drawing and the claims removed.

0018drawing

0019In the drawing, an embodiment of the fuel injection valve according to the invention is shown. It shows

00201 shows a longitudinal section through a fuel injection valve according to the invention,

0021FIG. 2 shows an enlargement of FIG. 1 in the area denoted by II,

0022FIG. 3 shows an enlargement of FIG. 1 in the area designated III,

0023Figure 4 shows the same section as Figure 3, wherein the outer piston rod is in a different switching position. Description of the embodiment

00241 shows an embodiment of the fuel injection valve according to the invention is shown in longitudinal section. The fuel injection valve comprises a housing 1, which may be constructed in several parts. The housing 1 has at its combustion chamber end portion a bore 3, in which a piston-shaped outer valve needle 10 is arranged. The outer valve needle 10 is sealingly guided in a bore away from combustion chamber in the bore 3 and tapers to form a pressure shoulder 9 to the combustion chamber. At the combustion chamber end, the outer valve needle 10 passes into a conical pressure surface 101 and finally into a likewise conical valve sealing surface 11, wherein the sealing surface 11 comes into abutment in the closed position of the outer valve needle 10 at a formed on the combustion chamber end of the bore 3 valve seat 13. FIG. 2 shows an enlarged view of the section of FIG. 1 designated by II in the region of the valve seat 13. By a radial extension of the bore 3, a pressure chamber 5 is formed in the housing 1 at the level of the pressure shoulder 9, which continues as a valve surrounding the outer valve 10 annular channel to the valve seat 13. In the valve seat 13 a plurality of injection openings 7 are formed, which are arranged in a first row of injection openings 107 and in a second row of injection openings 207 arranged offset axially thereto. When the outer valve needle 10 abuts the valve seat 13, it closes all the injection openings 7 against the pressure chamber 5, so that no fuel can reach the injection openings 7 from it.

0025In the outer valve needle 10, an inner valve needle 12 is arranged, which is piston-shaped and which has a conical pressure surface 112 and a valve sealing surface 14 at its combustion chamber end. If the inner valve needle 12 abuts against the valve seat 13, the valve sealing surface 14 contacts the valve seat 13 between the first injection opening row 107 and the second injection opening row 207. The interaction of the outer valve needle 10 and the inner valve needle 12 allows the injection opening rows 107, 207 connect to the pressure chamber 5. If the outer valve needle 10 is in contact with the valve sealing surface 11 on the valve seat 13, then both rows of injection openings 107, 207 are closed against the pressure chamber 5. Only lifts the outer valve needle 10 off the valve seat 13, while the inner valve needle 12 abuts with the valve sealing surface 14 on the valve seat 13, only the first row of injection openings 107 is connected to the pressure chamber 5, while the second row of injection openings 207 remains closed by the inner valve needle 12. Only when the inner valve needle 12 lifts off from the valve seat 13, the second Einspritzöff- series 207 is connected to the pressure chamber 5.

0026About a running in the housing 1 inlet channel 15 of the pressure chamber 5 is connected to a high-pressure port 17 which is connected to a high-pressure fuel source, not shown in the drawing. The high-pressure fuel source in this case provides during operation of the internal combustion engine, a predetermined high-pressure fuel, so that in the inlet channel 15 and thus also in the pressure chamber 5 always this fuel pressure prevails and forms a high-pressure fuel area.

0027Facing away from the combustion chamber to the bore 3, a piston bore 18 embodied as a blind bore is formed in the housing 1 and has a base surface 19. In the piston bore 18, an outer piston rod 20 is arranged longitudinally displaceable, which abuts with its combustion chamber facing the end face on the outer valve needle 10 and the combustion chamber with its front end 21 a formed at the end of the piston bore 18 control chamber 24 limited. By a radial enlargement of the piston bore 18, a spring chamber 8 is formed in the housing 1 at the combustion chamber end region of the piston rod 20, in which a spring 42 is arranged under pressure prestressing. The spring 42 is supported fixedly at the end facing away from the combustion chamber and bears against a spring plate 44, which is connected to the outer piston rod 20, at its end facing the combustion chamber.

0028In the outer piston rod 20, an inner piston rod 22 is arranged, which is longitudinally displaceable in the outer piston rod 20. At its end facing the combustion chamber, the inner piston rod 22 abuts on the inner valve needle 12, so that the inner piston rod 22 and the inner valve needle 12 move synchronously. Figure 3 shows an enlargement of Figure 1 in the region of the control chamber 24. The control chamber 24 is bounded by the base 19, the wall of the piston bore 18 and the end face 21 of the outer piston rod 20. The outer piston rod 20 has an inwardly cantilevered region 27 at its end remote from the combustion chamber, so that an inner control chamber 29 is delimited by the outer piston rod 20 and the end face 31 of the inner piston rod facing away from the combustion chamber. which is connected via a connecting bore 28 in the outer piston rod 20 with the control chamber 24. Inside the outer piston rod 20, a stop surface 23 is formed which limits the longitudinal movement of the inner piston rod 22. In the closed position of the fuel injection valve, that is, when both the inner valve needle 12 and the outer valve needle 10 abut the valve seat 13, an axial distance remains between the stop surface 23 and the combustion chamber facing away end face 31 of the inner piston rod 22. The control chamber 24 is via an inlet throttle 25 connected to the inlet channel 15. In addition, the control chamber 24 is connected via an outlet throttle 25 with a formed in the housing 1 leakage oil chamber 30. In the leakage oil chamber 30, a longitudinally movable armature 34 is arranged, having at its the control chamber 24 end facing a sealing ball 32. The armature 34 is acted upon by a closing spring 38, which presses the armature 34 in the direction of the control chamber 24. Further, in the leakage oil chamber 30, an electromagnet 36 is arranged, which exerts an attractive force on the magnet armature 34 with appropriate energization and moves it away from the control chamber 24 against the force of the closing spring 38. If the electromagnet 36 is not energized, then the armature 34 is pressed by the closing spring 38 in the direction of the control chamber 24, and the sealing ball 32 closes the outlet throttle 26. When current is supplied to the electromagnet 36, the armature 34 is moved away from the control chamber 24 and the sealing ball 32 is the outlet throttle 26 free. In this position, fuel can flow from the control chamber 24 into the leakage oil chamber 30 via the outlet throttle 26. The magentanker 34, the sealing ball 32 and the electromagnet 36 thus form a valve 33.

0029The operation of the fuel injection valve is as follows: In the closed state of Kraftstoffeinspritzven- tils, so if no fuel is injected through the injection openings 7 in the combustion chamber of the internal combustion engine, the sealing ball 32 closes the outlet throttle 26. By the inlet throttle 25 prevails in the control chamber 24 of the same This results in a hydraulic force on the end face 21 of the outer piston rod 20 and on the end face 31 of the inner piston rod 22, which transmit these to the outer valve needle 10 and the inner valve needle 12, so that the valve needles 10th , 12 are pressed into contact with the valve seat 13 and close the injection openings 7. The size ratio of the end face 21 to the pressure shoulder 9 or the pressure surface 101 of the outer valve needle 10 is designed so that in this state of the fuel injection valve, the hydraulic force on the end face 21 of the outer piston rod 20 outweighs. If an injection of fuel into the combustion chamber, so the electromagnet 36 is energized, causing the armature 34 and thus also the sealing ball 32 move away from the outlet throttle 26 and connect via the outlet throttle 26 the control chamber 24 with the leakage oil chamber 30. The flow resistances of inlet throttle 25 and outlet throttle 26 are designed so that the fuel pressure thereby drops in the control chamber 24, and so far,

0030As soon as the outer valve needle 10 lifts off from the valve seat 13, it releases the first row of injection openings 107, through which fuel is now injected into the combustion chamber of the internal combustion engine. As a result, the pressure surface 112 of the inner valve needle 12 is now acted upon by the fuel pressure of the pressure chamber 5, so that the inner valve needle 12 experiences an opening force. However, the remaining fuel pressure in the control chamber 24 is so high that the hydraulic force on the end face 31 of the inner piston rod 22 is still sufficient to keep the inner valve needle 12 against the opening force in the closed position. In the course of the opening stroke, the outer piston rod 20 finally comes to the base 19 to the system, whereby the control chamber 24 through an additional throttle 45, which forms between the end face 21 of the outer piston rod 20 and the base 19, is largely closed against the outlet throttle 26. This position of the outer piston rod 20 is shown in FIG. As a result, the further inflow of fuel from the control chamber 24 is reduced to the outlet throttle 26, and the pressure in the inner control chamber 29 drops further. Due to the now lower hydraulic pressure in the inner control chamber 29, driven by the hydraulic force on the pressure surface 112, the inner valve needle 12 and thus also the inner piston rod 22 moves away from the valve seat 13 so that the second injection opening row 207 is opened. The inner piston rod 22 moves in the axial direction until it comes to rest on the abutment surface 23 of the outer piston rod 20. As a result of the successive opening up of the two rows of injection openings 107 and 207, an injection progression is achieved in which fuel is injected into the combustion chamber of the internal combustion engine at full pressure, but only through part of the injection openings 7 at the beginning of the injection, while through the main injection Injection openings 7 of both rows of injection openings 107 and 207 is injected and thus with a higher injection rate. In order to terminate the injection process, the energization of the electromagnet 36 is stopped and, driven by the closing spring 38, the sealing ball 32 on the magnet armature 34 closes the drainage throttle 26,

0031It can also be provided to inject fuel only through the first row of injection openings 107. For this purpose, the valve 33, which is formed by the electromagnet 34, the armature 34 and the sealing ball 32, closed again before the fuel pressure in the control chamber 24 has dropped so far that the inner valve needle 12 opens. The outlet throttle 26 is then already closed again before the outer piston rod 20 comes to rest with the end face 21 on the base 19 of the piston bore 18. This results between the end face 21 and the base 19, a hydraulic cushion which dampens the opening movement of the outer piston rod 20 and prevents a pressure drop in the control chamber 24, so that the inner piston rod 22 always exerts a sufficient closing force on the inner valve needle 12.

0032It can also be provided that the outer piston rod 20 during the opening stroke of the outer valve needle 10, the inlet throttle 25 partially covers, so that the cross section of the inlet throttle 25 is reduced, but this is not completely closed. This can be realized for example by a remaining annular gap between the outer piston rod 20 and the wall of the piston bore 18. The connection of the control chamber 24 with the outlet throttle 26 is ensured, for example, by grooves extending in the radial direction on the end face 21 of the outer piston rod 20. As a result, the fuel flow through the inlet throttle 25 in the control chamber 24 is significantly reduced, so that the Kraf material pressure in the control chamber 24 and, via the communication bore 28,