EP2249024B1 - Fuel injector - Google Patents

Abstract

Fuel injector (7) comprises a valve group (2) arranged between a nozzle needle (6) and an actuator (3), a valve piston (16) arranged in a hole (32) for moving between a closed and an injection position, a control space (14) for moving the valve piston, a valve chamber (24) arranged between the valve piston and the valve group and an inlet (25) and an outlet (27) opening into the valve chamber. Preferred Features: The actuator is a piezo-electric actuator. The valve chamber is formed in the valve hole radially around the valve piston.

Description

The invention relates to an actuator-controlled fuel injector.

State of the art

Fuel injectors in which a nozzle needle is actuated by an actuator to open and close an injection port are known in the art, see example as WO 2008/017538 A1 , In order to realize the necessary stroke of the nozzle needle, such injectors must have a certain minimum length, which can not be fallen below. Such a minimum length limits the capabilities of the injector and causes increased manufacturing and assembly costs.

In order to reduce the length at a given stroke of the nozzle needle, injectors are known in which two actuators are connected in series. Injectors with multiple actuators connected in series are complex and expensive to manufacture.

Disclosure of the invention

An object of the invention is to provide a simple and inexpensive to produce injector, which has the shortest possible length with the largest possible stroke of the nozzle needle.

The object is solved by the subject matter of the independent claim. Advantageous developments emerge from the dependent claims.

An injector according to the invention for injecting fuel into a combustion chamber of an internal combustion engine has a valve group which is located between a nozzle needle and an actuator, wherein a valve piston bore is formed in the valve group; a valve piston disposed in the valve piston bore that passes through the actuator between a closed position and at least one injection position is movable; a nozzle needle control space whose volume is variable by moving the valve piston; a valve space formed between the valve piston and the valve group and connected to the nozzle needle control space via a servo bore formed in the valve piston; an inlet and a drain, which open into the valve chamber, wherein the mouth of the drain is closed in the valve chamber by the valve piston when the valve piston is in the closed position and wherein the mouth of the drain is open, when the valve piston in a Injection position is located.

In such an injector according to the invention, the necessary stroke of the nozzle needle can be realized with an actuator whose length is significantly reduced compared to a conventional injector. The costs for the actuator can therefore be significantly reduced. Also, the drain can be made smaller than in a conventional injector, so that the control amount can be reduced.

In one embodiment, the valve piston bore has a lower portion facing the nozzle needle and an upper portion facing the actuator, the lower portion having a larger cross-section than the upper portion. The valve piston has a lower portion facing the nozzle needle and an upper portion facing the actuator, wherein the lower portion has a larger cross section than the upper portion and is fitted in the lower portion of the valve piston bore, that between the lower portion of the valve piston and the valve group is formed a second control chamber.

In one embodiment, the second control chamber has a larger cross-section than the nozzle needle control chamber. By such a structure can be easily and reliably achieve a reversal of motion between the actuator and the nozzle needle, so that the actuator is activated during the injection process, that is lengthened. Such a direct-acting injector has a good durability and a low drift of the Aktohubes.

In one embodiment, a control chamber bore is formed in the valve piston, which hydraulically connects the nozzle needle control chamber with the second control chamber. Such a control chamber bore allows effective pressure equalization between the nozzle needle control chamber and the second control chamber.

In one embodiment, the valve space between the nozzle needle and the valve piston is arranged. In particular, the valve space is formed radially around the valve piston in the valve piston bore. This allows a particularly simple arrangement of the valve chamber and an easy-to-implement design of the inlet and outlet, which open into the valve piston bore.

According to the invention, when the valve piston is in an injection position, the valve piston wipes the mouth of the inlet into the valve chamber, and the mouth of the inlet is opened when the valve piston is in the closed position. Characterized in that the inlet is closed when the valve piston is in the injection position, the pressure in the valve chamber during the injection process drops very quickly. This causes a particularly fast movement of the nozzle needle when opening the injection openings and allows very short switching and injection times.

In one embodiment, a servo box is formed in the servo bore. In a further embodiment, an inlet or outlet throttle is formed in the inlet and / or in the outlet. By means of such throttles, a desired opening and closing behavior of the nozzle needle can be adjusted particularly well. A suitable servo throttle in the servo bore allows the servo influence to be superimposed on the direct needle stroke with a time delay. As a result, a better injection quality is achieved, in particular when injecting small amounts, in which a high injection tolerance and a fast switching is required. This leads to lower exhaust emissions and reduced consumption.

In one embodiment, the actuator facing the end of the valve piston is connected to a coupler piston. The coupler piston is fitted into a coupler sleeve connected to the actuator such that between the coupler piston and the coupler sleeve is formed a coupler space. The coupler space makes it possible to compensate for temperature-induced changes in length of the components.

In one embodiment, the actuator is a piezoelectric actuator. Piezoelectric actuators are particularly reliable and have particularly short reaction times, which enable particularly fast injection processes with short switching times.

• Figur 1 zeigt einen Schnitt durch ein Ausführungsbeispiel eines erfindungsgemäßen Injektors.
• Figur 2 zeigt die Ventilgruppe des Injektors aus Figur 1 im geschlossenen Zustand.
• Figur 3 zeigt die Ventilgruppe des Injektors aus Figur 1 in einem geöffnetem Zustand.
• Figur 4 zeigt ein alternatives Ausführungsbeispiel der Ventilgruppe, bei der der Zulauf stets geöffnet ist.
• Figur 5 zeigt ein weiteres Ausführungsbeispiel der Ventilgruppe mit einer zusätzlichen Servodrossel.

The structure and operation of an injector according to the invention will be explained in more detail below with reference to the embodiments described in more detail in the accompanying figures. Showing:

• FIG. 1 shows a section through an embodiment of an injector according to the invention.
• FIG. 2 shows the valve group of the injector FIG. 1 in the closed state.
• FIG. 3 shows the valve group of the injector FIG. 1 in an open state.
• FIG. 4 shows an alternative embodiment of the valve group, in which the inlet is always open.
• FIG. 5 shows a further embodiment of the valve group with an additional servo throttle.

The structure and operation of a first embodiment of an injector according to the invention are described below with reference to FIGS. 1 to 3 explained in more detail.

FIG. 1 shows a section through an embodiment of an injector 7 according to the invention. FIG. 2 shows an enlarged view of the valve group of in FIG. 1 shown injector 7 in the closed state. FIG. 3 shows an enlarged view of the valve group in an open state.

An inventive injector 7 has a in the FIG. 1 Shown above cylindrical injector body 4 and in the FIG. 1 shown below cylindrical nozzle module 1, which are clamped by a hydraulic nozzle lock nut 58 hydraulically tight. The connection between the nozzle retaining nut 58 and the injector body 4 is additionally sealed by a sealing ring 60.

In the nozzle module 1, a nozzle needle chamber 56 and a fuel chamber 52 are formed, which are hydraulically connected to each other via at least one connecting bore 54. Two injection openings 8 connect the fuel chamber 52 with a combustion chamber 5, which surrounds the lower end of the nozzle module 1. Along a longitudinal axis A of the nozzle module 1, a nozzle needle 6 is arranged in the nozzle needle chamber 56 and in the fuel chamber 52, which is movable parallel to a longitudinal axis A of the nozzle module 1 between a lower closure position and at least one upper injection position. A lower closing end 10 of the nozzle needle 6 closes the injection openings 8 when the nozzle needle 6 is in the lower closing position, and releases the injection openings 8 when the nozzle needle 6 is in an upper injection position. In operation, the nozzle needle chamber 56 and the fuel chamber 52 are filled with pressurized fuel. When the injection openings 8 are released, the fuel flows from the fuel chamber 52 through the injection openings 8 into the combustion chamber 5.

An upper control end 6a of the nozzle needle 6 is movably arranged in a control chamber sleeve 15. A nozzle needle spring 12 is arranged around an upper region of the nozzle needle 6 and is supported, on the one hand, on a shoulder 11 formed on the circumference of the nozzle needle 6 and, on the other hand, on the control chamber sleeve 15. Thus, the nozzle needle 6 is mounted elastically movable parallel to the longitudinal axis A in the nozzle module 1 and is pressed by the nozzle needle spring 12 in the lower closure position in which it closes the injection openings 8.

Above the nozzle module 1, a valve group 2 is pressure-tight in the nozzle retaining nut 58 fitted. In the valve group 2, a valve piston bore 32 is formed, in which a valve piston 16 is inserted so that it is movable parallel to the longitudinal axis A of the injector 7.

Within the control chamber sleeve 15, a nozzle needle control chamber 14 is formed, which is bounded on the one hand by the nozzle needle 6, on the other hand by the valve piston 16 and the volume of both by moving the nozzle needle 6 as well can be varied by moving the valve piston 16 parallel to the longitudinal axis A of the injector 7.

The valve piston 16 has a lower portion 16a facing the nozzle needle 6 and an upper portion 16b facing away from the nozzle needle 6. The lower portion 16 a of the valve piston 16, in a plane which is aligned at right angles to the longitudinal axis A of the injector 7, a larger cross-section than the upper portion 16 b of the valve piston 16 and is fitted in such a manner in the lower portion of the valve piston bore 32 that on from the nozzle needle 6 side facing away from the lower portion 16a of the valve piston 16 between the valve piston 16 and the valve group 2, a second control chamber 22 is formed, the volume of which is variable by moving the valve piston 16 parallel to the longitudinal axis A. The second control chamber 22 is hydraulically connected to the nozzle needle control chamber 14 through a control chamber bore 20 which extends through the lower portion 16 a of the valve piston 16.

Around the upper region 16b of the valve piston 16, a valve space 24 is formed between the valve piston 16 and the valve group 2 in the valve piston bore 32, which radially surrounds the valve piston 16. The valve chamber 24 is hydraulically connected to the nozzle needle control chamber 14 by a servo bore 18 formed in the valve piston 16. An inlet 25 hydraulically connected to a fuel feed line 38 opens below valve space 24 in the valve piston bore 32. The fuel feed line 38 is connected to a fuel pump 39, which feeds fuel under high pressure via the fuel feed line 38 into the inlet 25 and via a bore formed in the nozzle module 43 the nozzle needle chamber 56 and through the connecting bore 54 and the fuel chamber 52 filled with fuel.

A drain 27 connected to a fuel drain passage 34 terminates above the valve space 24 in the valve piston bore 32. The fuel drain passage 34 is configured to discharge fuel from the injector 7 into a fuel intake device 36.

Below the mouth of the drain 27 into the valve piston bore 32, a sealing seat 30 is formed, which can be opened and closed by moving the valve piston 16 parallel to the longitudinal axis A of the injector 7 and so that by moving the valve piston 16, a hydraulic connection between the drain 27 and the valve chamber 24 can be produced and closed. The hydraulic connection between the valve chamber 24 and the drain 27 is closed when the valve piston 16 is in the upper, closed position and the hydraulic connection is opened when the valve piston 16 is in a lower injection position.

In the upper area 16b of the valve piston 16, a recess 17 is formed around its circumference such that the inlet 25 is hydraulically connected to the valve space 24 when the valve piston 16 is in the upper, closed position, and the valve space 24 hydraulically from the inlet 25 is disconnected when the valve piston 16 is in a lower injection position.

The upper, remote from the nozzle needle 6 end of the valve piston 16 protrudes beyond the upper, remote from the nozzle needle 6 end of the valve assembly 2 addition. At a top, remote from the nozzle needle 6 end face of the valve piston 16, a coupler piston 48 is mounted, which is fitted in such a manner arranged above the valve group 2 coupler 44, that between the coupler piston 48 and the coupler 44, a coupler 46 is formed in the Operation is filled with fuel. The volume of the coupler space is variable by moving the coupler piston 48 and / or by moving the coupler sleeve 44.

The coupler sleeve 44 is surrounded by a coupler spring 50, which supports the coupler sleeve 44 elastically and parallel to the longitudinal axis A movable on the valve group 2.

The coupler sleeve 44 is mechanically coupled to an actuator module 3, which is arranged on the side facing away from the valve group 2 side of the coupler sleeve 44, such that the coupler sleeve 44 by pressing the actuator module 3 against the force of the coupler spring 50 is movable parallel to the longitudinal axis A of the injector 7.

In the closed state of the injector 7, i. if no fuel is to be injected into the combustion chamber 5, the actuator 3 is de-energized. The coupler sleeve 44, the coupler piston 48 and the valve piston 16 are each in an upper position. The sealing seat 30 between the valve chamber 24 and the drain 27 is closed. The valve chamber 24 is in hydraulic communication with the inlet 25, so that in the valve chamber 24, the high system pressure of the fuel system prevails. The valve chamber 24 is in hydraulic communication with the nozzle needle control chamber 14 via the servo bore 18, so that the high fuel pressure also prevails in the nozzle needle control chamber 14. The nozzle needle 6 is pressed by the nozzle needle spring 12 and the pressure prevailing in the nozzle needle control chamber 14 fuel pressure in the lower, closed position in which the nozzle seat 10, the injection ports 8 closes and no fuel from the fuel chamber 52 flows into the combustion chamber 5.

To initiate an injection process, the actuator 3 is activated by applying an electrical voltage to an electrical connection 40. The actuator 3 extends and pushes the coupler piston 44 against the force of the coupler spring 50 in the direction of the valve group 2 down. As a result of the force exerted on the volume of the coupler space 46, the coupler piston 48 is also pressed in the direction of the valve group 2.

The coupler piston 48 pushes the valve piston 16 within the valve piston bore 32 in the direction of the nozzle needle 6 down. As a result, on the one hand, the volume of the nozzle needle control chamber 14 is reduced, on the other hand, the volume of the second control chamber 22 is increased. There, as in particular in the FIG. 2 1, the cross section A1 of the second control chamber 22 is greater than the cross section A2 of the nozzle needle control chamber 14, and the second control chamber 22 is hydraulically connected to the nozzle needle chamber 14 through the control chamber bore 20, the total volume, ie the sum of the volumes of the two control chambers 14, increases , 22, so that the pressure of the fuel in the two control chambers 14, 22 decreases.

The reduced pressure in the nozzle needle control chamber 14 is insufficient to keep the nozzle needle 6 in the lower, closed position against a force of the fuel in the fuel chamber 52 acting on a pressure stage 9 formed in the lower portion of the nozzle needle 6. The nozzle needle 6 moves upward under the influence of the force acting on the pressure stage 9. The nozzle seat 10 is opened and fuel from the fuel chamber 52 flows through the injection openings 8 into the combustion chamber 5.

If dAH is the stroke of the coupler piston 44, A1 is the cross section of the second control chamber 22 and A2 is the cross section of the nozzle needle control chamber 14, the direct stroke of the nozzle needle 6 caused by the change in the total volume of the control chambers 14, 22 is dNH: $$\mathrm{DNH}\mathrm{=}\left(\mathrm{A}\mathrm{1}\mathrm{-}\mathrm{A}\mathrm{2}\right)\mathrm{/}\mathrm{A}\mathrm{2}\mathrm{*}\mathrm{dAH}$$

By selecting the cross sections A1 and A2 of the control chambers 14, 22, the ratio dNH / dAH = (A1-A2) / A2 between the stroke of the coupler piston 44 and the direct stroke of the nozzle needle 6 is adjusted as needed.

With the direct stroke in particular small strokes for injecting small amounts of fuel, which require a high injection tolerance and short switching times, can be realized with high quality. This has a positive effect on emissions and consumption.

In addition, when the valve piston 16 moves downward to initiate the injection operation by the coupler piston 48 in the valve piston bore 32, the seal seat 30 between the valve chamber 24 and the drain 27 is opened. Fuel from the nozzle needle control chamber 14 flows through the servo bore 18, the valve chamber 24, the open seal seat 30 and the drain 27 into the drain passage 34.

As soon as the valve piston 16 has moved downwards by the slide stroke SH, the mouth of the inlet 25 into the valve chamber 24 is closed by the valve piston 16, so that no additional fuel from the supply line 38 flows into the valve chamber 24.

The opening of the drain 27 and the closing of the inlet 25 causes, in addition to the previously described increase in the total volume of the control chambers 14 and 22, a further reduction in the pressure in the nozzle needle control chamber 14, whereby an additional upward force acts on the nozzle needle 6. This additional force accelerates the nozzle needle 6 in addition to the direct stroke dNH, which results from the volume change of the control chambers 14, 22, so that the injection openings 8 are opened further and faster. As a result, shorter injection times can be realized.

To end the injection process, the voltage applied to the actuator 3 is turned off. The length of the actuator 3 decreases and the coupler sleeve 44 is pressed by the coupler spring 50 against the shortened actuator 3 upwards in the direction of the shortened actuator 3. The pressure in the coupler chamber 46 decreases, and the coupler piston 48 and the valve piston 16 connected to it move upwards in the direction of the actuator 3.

Since the volume of the second control chamber 22 is more reduced by the upward movement of the valve piston 16, as the volume of the Düsennadelsteuerraums 14 increases (direct stroke dNH), fuel flows through the control chamber bore 20 from the second control chamber 22 in the nozzle needle control chamber 14 and increases the pressure in the nozzle needle control room 14.

By the upward movement of the valve piston 16, the sealing seat 30 is closed in the valve piston bore 32, so that no further fuel flows through the outlet 27 from the valve chamber 24 into the drainage channel 34. At the same time the mouth of the inlet 25 is opened in the valve chamber 24. Fuel under high pressure flows from the supply line 38 into the valve chamber 24. Via the servo bore 18 formed in the valve piston 16, fuel passes from the valve chamber 24 into the nozzle needle control chamber 14 and additionally increases the pressure in the nozzle needle control chamber 14.

The increased pressure in the nozzle needle control chamber 14 causes a downward force on the nozzle needle 6, which is sufficient to press the nozzle needle 6 against the force acting on the pressure step 9 upward force in the nozzle seat 10 and to close the injection openings 8. No further Fuel flows through the injection openings 8 from the fuel chamber 52 into the combustion chamber 5 and the injection process is completed.

By a suitable dimensioning of a feed throttle 26 formed in the inlet 25 and a flow restrictor 28 formed in the drain 27, the opening speed and the closing speed of the nozzle needle 6 can be adjusted as required.

FIG. 4 shows an alternative embodiment of the valve assembly according to the invention. In this embodiment, the inlet 25 opens directly into the valve chamber 24. The hydraulic connection of the inlet 25 with the valve chamber 24 is not interrupted during the injection process. By a suitable dimensioning of the inlet throttle 26 so the opening speed of the nozzle needle 6 can be adjusted. In particular, the nozzle needle 6 can be braked when opening, to prevent the nozzle needle 6 opens faster than desired.

FIG. 5 shows a further alternative embodiment of the valve group 2 according to the invention, wherein in the servo bore 18 of the valve piston, a servo throttle 19 is formed. By suitable dimensioning of the servo throttle 19, the servo influence on the direct needle stroke dNH, which results from the change in the volume of the nozzle needle control chamber 14 and the second control chamber 22, can be superimposed with a time delay. As a result, a better injection quality is achieved, in particular when injecting small amounts, in which a high injection tolerance and a fast switching is required. This leads to lower exhaust emissions and reduced consumption.

Claims (9)

1. Injector (7) for injecting fuel into a combustion chamber (5) of an internal combustion engine, having a valve group (2) which is situated between a nozzle needle (6) and an actuator (3), wherein a valve piston bore (32) is formed in the valve group (2); having a valve piston (16) which is arranged in the valve piston bore (32) and which can be moved by the actuator (3) between a closed position and at least one injection position; having a nozzle needle control chamber (14) whose volume can be varied by means of the movement of the valve piston (16); having a valve chamber (24) which is formed between the valve piston (16) and the valve group (2) and which is connected via a servo bore (18) formed in the valve piston (16) to the nozzle needle control chamber (14), to an inlet (25) and to an outlet (27) which open into the valve chamber (24), wherein the opening of the outlet (27) into the valve chamber (24) is closed off by the valve piston (16) when the valve piston (16) is situated in the closed position, and wherein the opening of the outlet (27) is open when the valve piston (16) is situated in an injection position, characterized in that the opening of the inlet (26) into the valve chamber (24) is closed by the valve piston (16) when the valve piston (16) is situated in an injection position, and in that the opening of the inlet (25) is open when the valve piston (16) is situated in the closed position.
2. Injector (7) according to Claim 1, wherein the valve piston bore (32) has a lower region facing towards the nozzle needle (6) and has an upper region facing towards the actuator (3), wherein the lower region has a larger cross section than the upper region, and wherein the valve piston (16) has a lower region facing towards the nozzle needle (6) and has an upper region facing towards the actuator (3), wherein the lower region has a larger cross section than the upper region and is thus fitted into the lower region of the valve piston bore (32), such that a second control chamber (22) is formed between the lower region of the valve piston (16) and the valve group (2).
3. Injector (7) according to Claim 2, wherein the second control chamber (22) has a larger cross section than the nozzle needle control chamber (14).
4. Injector (7) according to Claim 2 or 3, wherein a control chamber bore (20) is formed in the valve piston (16), which control chamber bore connects the nozzle needle control chamber (14) to the second control chamber (22).
5. Injector (7) according to one of Claims 1 to 4, wherein the valve chamber (24) is formed between the nozzle needle (6) and the valve piston (16).
6. Injector (7) according to Claim 5, wherein the valve chamber (24) is formed radially around the valve piston (16) in the valve piston bore (32).
7. Injector (7) according to one of Claims 1 to 6, wherein at least one throttle (18, 26, 28) is formed in the servo bore (17), in the inlet (25) and/or in the outlet (27).
8. Injector (7) according to one of Claims 1 to 7, wherein that end of the valve piston (16) which faces towards the actuator (3) is connected to a coupler piston (48), said coupler piston being fitted into a coupler sleeve (44), which is connected to the actuator (3), in such a way that a coupler chamber (46) is formed between the coupler piston (48) and the coupler sleeve (44).
9. Injector (7) according to one of Claims 1 to 8, wherein the actuator (3) is a piezoelectric actuator (3).

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