Fuel Injector

Abstract

A fuel injector includes an injector housing, a longitudinally movable nozzle needle, and a force sensing element. The injector housing defines a nozzle chamber, a pressure chamber, and a measuring chamber. The nozzle chamber is configured to be supplied with pressurized fuel via a feed line formed in the injector housing. The pressure chamber is configured to be hydraulically connected to the feed line. The nozzle needle is disposed in the nozzle chamber and is configured to open and to close at least one spray hole. The force sensing element is disposed in the measuring chamber and is configured to detect a pressure in the pressure chamber. The measuring chamber is separated from the pressure chamber by a diaphragm-like intermediate wall. The force sensing element supports the intermediate wall.

Claims

1. A fuel injector, comprising: an injector housing defining a nozzle chamber, a pressure chamber, and a measuring chamber the-nozzle chamber configured to be supplied with pressurized fuel via a feed line formed in the injector housing, the pressure chamber configured to be hydraulically connected to the feed line, a longitudinally movable nozzle needle disposed in the nozzle chamber, and configured to open and to close at least one spray hole, and a force sensing element disposed in the measuring chamber and configured to at least indirectly detect a pressure in the pressure chamber wherein the measuring chamber is separated from the pressure chamber by a diaphragm-like intermediate wall, and wherein the force sensing element supports the intermediate wall.

2. The fuel injector as claimed in claim 1, wherein the force sensing element is preloaded against the intermediate wall.

3. The fuel injector as claimed in claim 2, wherein the force sensing element is preloaded by a screw element.

4. The fuel injector as claimed in claim 2, wherein the force sensing element is preloaded by an overdimension located inside the injector housing.

5. The fuel injector as claimed in claim 1, wherein the force sensing element comprises a piezoelectric force sensing element.

6. The fuel injector as claimed in claim 1, further comprising: a connected bore configured to connect e pressure chamber to the nozzle chamber.

7. The fuel injector as claimed in claim 1, further comprising: a control chamber, wherein a longitudinal movement of the nozzle needle is controlled by a pressure in the control chamber.

8. The fuel injector as claimed in claim 7, further comprising: a tap hole configured to connect the pressure chamber to the control chamber.

9. The fuel injector as claimed in claim 7, further comprising: a pilot valve forming a valve chamber and configured to control the pressure in the control chamber; and a return throttle configured to connect the control chamber to the valve chamber.

10. The fuel injector as claimed in claim 9, further comprising: a channel configured to connect the pressure chamber to the valve chamber.

11. The fuel injector as claimed in claim 1, wherein the teed line is connected to the pressure chamber.

12. The fuel injector as claimed in claim 1, further comprising: a nozzle clamping nut, wherein the injector housing includes a nozzle body, a throttle plate, a valve plate, and a retaining body, and wherein the nozzle clamping nut is configured to brace together the nozzle body, the throttle plate, the valve plate, and the retaining body.

13. The fuel injector as claimed in claim 12, further comprising: a pilot valve including a pilot valve seat disposed on the valve plate and configured to control the nozzle needle, wherein the valve plate forms the measuring chamber.

14. The fuel injector as claimed in claim 13, wherein: the throttle plate forms the measuring chamber; and the throttle plate delimits the nozzle chamber.

Description

[0020] Further advantages, features and details of the invention are apparent from the following description of preferred exemplary embodiments, and from the drawings, in which:

[0021] FIG. 1 shows a longitudinal section through a fuel injector according to the invention with a force sensing element for detecting a pressure or for detecting pressure fluctuations, only the essential regions being represented,

[0022] FIG. 2 shows a section of a further exemplary embodiment of the fuel injector in longitudinal section, only the essential regions being represented,

[0023] FIG. 3 shows a section of another further exemplary embodiment of the fuel injector in longitudinal section, only the essential regions being represented,

[0024] FIG. 4 shows the bracing concept of the force sensing element inside the fuel injector.

[0025] Like elements or elements having the same function are provided in the Figures with the same reference numerals.

[0026] FIG. 1 shows a fuel injector 1 according to the invention 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.

[0027] 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 10a adjoined by a throttle plate 10b which in turn is a adjoined on the side facing away from the nozzle body 10a by a valve plate 10c and a retaining body 10d. These components of the injector housing 10 are braced together axially in a sealing manner by a nozzle clamping nut 10e.

[0028] 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 10a. The nozzle body 10a 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.

[0029] 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 10a.

[0030] The nozzle needle 2 is guided radially in the nozzle chamber 6 by the nozzle body 10a, 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 10b 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 10b. The sleeve 36 is tensioned against the throttle plate 10b 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.

[0031] 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 10c, 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 10b. 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 10c and in the throttle plate 10b. In alternative embodiments, however, the valve chamber 20 may have any desired form.

[0032] According to the invention, 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 17a 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.

[0033] 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 10c and is connected to the control chamber 4 via a tap hole 12 formed in the throttle plate 10b.

[0034] Furthermore, a measuring chamber 16 is formed in the valve plate 10c 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.

[0035] The measuring chamber 16 is the form of a blind hole open towards the retaining body 10d. 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 10d or, as in the exemplary embodiment of FIG. 1, by means of a screw element 18 screwed into the measuring chamber 16.

[0036] 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.

[0037] Further embodiments of the fuel injector 1 according to the invention are described below. Regions not described in detail are implemented as in the exemplary embodiment of FIG. 1.

[0038] 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 10c, the blind hole being open towards the retaining body 10d. 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 10d and the intermediate wall 13, as the nozzle clamping nut 10e is tightened.

[0039] 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 10c and is delimited by the valve plate 10c and the throttle plate 10b. The pressure chamber 14 is connected to the valve chamber 20 via a channel 15 also formed in the valve plate 10c, so that the pressure prevailing in the valve chamber 20 is also present in the pressure chamber 14.

[0040] 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 101.

[0041] 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 10d and the intermediate wall 13. A connecting bore 32 is formed in the throttle plate 10b 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 10c, but may also be formed in the throttle plate 10b in alternative embodiments.

[0042] FIG. 4 shows a concept according to the invention 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 10d 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.

[0043] 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.

[0044] Furthermore, it is also alternatively possible to form the measuring chamber 16 in the throttle plate 10b, so that the force sensing element 17 is arranged within the throttle plate 10b. The force sensing element 17 can then be braced between the throttle plate 10b and the valve plate 10c, or between the throttle plate 10b and the retaining body 10d, in the event that the measuring chamber 16 is formed, for example, as a through-bore in the valve plate 10c.

[0045] The operation of the fuel injector 1 according to the invention is as follows:

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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 10c or in the throttle plate 10b. 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 wail 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.