EP2204570B1 - Fuel injector - Google Patents

Description

State of the art

The invention relates to a fuel injector for injecting fuel, in particular diesel or gasoline, into a combustion chamber of an internal combustion engine.

Common rail diesel injectors must open or close the flow cross section required for injection with high dynamics, so that fuel in the desired amount can flow into the combustion chamber. Due to the high fuel pressure (in future common-rail diesel systems up to 3000bar or more), the nozzle needle is pressed with great force into the nozzle needle seat. This hydraulic closing force must be overcome by the actuator of the nozzle needle when opening the fuel injector. Since the hydraulic closing force is so high in known Injektorkonzepten that direct actuation of the nozzle needle via an electromagnetic actuator is not possible, the nozzle needle is actuated hydraulically and / or via a piezoelectric actuator in today's fuel injectors via a servo circuit. Servo driven fuel injectors include a control chamber, the pressure of which is lowered by opening a servo valve. This requires a fuel return line, since the amount of tax incurred with open servo valve at low pressure level must be returned to the fuel tank. In addition, in principle occur in some fuel injector concepts permanent leakage, which must also be returned. Both control amount and leakage lead to a significant undesirable power loss in the fuel injector, since the corresponding volume of fuel must be brought in addition to the actual injection quantity at rail pressure level. This power loss must be provided by the high-pressure pump and thus reduces the efficiency of the entire system. Furthermore, the return amount causes additional heating of the fuel injector and increases due to the required low pressure line system overhead.

From the DE 27 102 16 A1 a fuel injector is known, which has two separate, successively openable fuel outlet regions. The nozzle needle of the known fuel injector is switchable, at least at pressures beyond 1800bar, either only by means of a piezoelectric actuator and / or a possibly electromagnetically actuated servo circuit.

Disclosure of the invention

The invention has for its object to provide a fuel injector in which the applied by an actuator opening force for adjusting the nozzle needle is minimized. Preferably, the fuel injector should manage without a fuel return port. More preferably, the fuel injector should be actuated by means of an electromagnetic actuator.

This object is achieved with a fuel injector having the features of claim 1. Advantageous developments of the invention are specified in the subclaims. All combinations of at least two features disclosed in the description, the claims and / or the figures fall within the scope of the invention.

The invention is based on the idea to associate the nozzle needle, preferably a nozzle needle tip, with a pressure equalization chamber delimited by the nozzle needle, whereby a hydraulic force acting in the opening direction on the nozzle needle is produced by establishing a hydraulic connection between the pressure equalization chamber and the pressure region the hydraulic closing force, at least partially, preferably completely, compensated, so that the opening force to be provided by the actuator for opening the nozzle needle, preferably to a minimum, is reduced. The pressure region preferably adjoins the nozzle needle on a nozzle needle side remote from the pressure equalization chamber. A pressure range of the fuel injector is understood to be the range in which injection pressure prevails at least approximately. Due to the provision of connectable by means of a valve with the pressure range of the fuel injector pressure compensation chamber can be dispensed with a low pressure region and thus to a fuel return port, which has a positive effect on the efficiency of the overall system. In particular, in a fuel injector designed according to the concept of the invention, all requirements for dynamics and spray quality can be met. By dispensing with a fuel return and the simple structure of the fuel injector, the system cost is reduced, resulting in a reduction in costs and a smaller space requirement. In addition, as indicated, the hydraulic power loss of the fuel injector significantly reduced because neither a leakage volume flow nor a control volume flow incurred. This reduces the amount of fuel to be delivered by the high-pressure pump, which enables a lower pump capacity. Particularly preferably, the valve for establishing the hydraulic connection between the pressure region and the pressure compensation chamber has a (substantially) smaller seat cross-section than the nozzle needle seat in order to ensure that the valve can be opened with a small actuator force. In the case of the embodiment of the fuel injector as a diesel injector, in particular as a common rail diesel injector, the pressure region which can be hydraulically connected to the pressure equalization chamber via the valve is preferably a high pressure region of the fuel injector the preferred at least approximately rail pressure prevails.

In addition to a design of the fuel injector as a diesel injector trained according to the concept of the invention injector can also be used for gasoline direct injection, wherein also in this case preferably at least approximately rail pressure prevails in the pressure range. Compared to known magnetically operated gasoline injectors can be achieved by the reduced actuation force significant dynamics advantages (shorter switching times). In addition, the nozzle needle seat diameter can be increased, which causes a smaller internal throttling with open fuel injector, so that almost immediately before the at least one injection port rests the full rail pressure. In addition to the comparatively expensive injectors with piezoelectric actuator costs can be saved.

In a further development of the invention is advantageously provided that no injection opening directly from the pressure equalization chamber. The pressure compensation chamber is preferably separated hydraulically from an opening region of the at least one injection opening, preferably all of the injection openings, by means of an annular gap seal. Particularly preferably, the fuel injector has only a single, in particular annular, discharge region, from which the at least one injection opening opens. Preferably, the injection opening is located in a region axially between a nozzle needle seat and the pressure compensation chamber. It is particularly preferred if the annular gap seal, the hydraulic pressure equalization space of the Ausmündungsbereich separates, radially between the nozzle needle and a nozzle body (housing part) is formed. Most preferably, the annular gap seal is a guide gap between the nozzle needle and the nozzle body.

As indicated above, an embodiment is particularly preferred in which the pressure compensation chamber is arranged and dimensioned such that the hydraulic closing force acting on the nozzle needle is completely compensated, so that the actuator essentially only has to overcome frictional forces and closing spring forces for opening the nozzle needle. To realize a perfect pressure balance of the nozzle needle in the axial direction, it is preferred if the diameter of the annular gap seal, ie preferably the diameter of the guide portion of the nozzle needle at least approximately, preferably corresponds exactly to the diameter of the nozzle needle seat.

Particularly preferred is an embodiment of the fuel injector, wherein the valve for establishing a hydraulic connection between the pressure region and the pressure equalization chamber opens before opening the nozzle needle. In other words, a hydraulic connection between the pressure region and the pressure equalization chamber is preferably produced before the start of the injection process, ie the hydraulic closing force is at least partially compensated in order then to be able to lift the nozzle needle from the nozzle needle seat with reduced actuator force. When the valve is open, in the case of the formation of the fuel injector as a diesel injector, fuel under high pressure flows into the pressure equalization chamber, especially below the nozzle needle, so that at least approximately rail pressure builds up in it, which then results in the desired pressure compensation of the nozzle needle causes. The pressure build-up is preferably accelerated by the fact that the aforementioned, preferred annular gap seal separates the pressure equalization chamber from the outlet region of the at least one injection opening, so that a significant flow of fuel from the pressure compensation chamber into the combustion chamber is prevented by the injection opening.

The closing of the fuel injector is preferably carried out by first moving the nozzle needle back into its nozzle needle seat and then closing the valve so as to again hydraulically separate the pressure compensation chamber from the pressure region of the fuel injector. Thus, in the closed state of the fuel injector, a complete tightness of the fuel injector given. As will be explained later, it is particularly preferred if the nozzle needle and the valve are assigned separate closing springs. By a suitable vote of the spring forces closing the nozzle needle can be ensured before the valve. Characterized in that the nozzle needle closes in front of the valve element of the valve, the displaced by the closing movement of the nozzle needle from the pressure compensation chamber fuel past the valve seat of the valve back into the pressure range.

The invention is advantageously provided that the fuel injector has a single actuator. This is preferably used both for adjusting the nozzle needle between its open and closed position and for opening and closing the valve. For this purpose, the actuator preferably acts both on a valve element of the valve and on the nozzle needle.

It is very particularly preferred in this case if the valve element, in particular mechanically, is coupled to the nozzle needle, preferably in such a way that the valve opens at a time-shifted adjustment of the nozzle needle from its closed position. In this case, preferably, the valve element or a component permanently connected to the valve element is designed as a driver, which entrains the nozzle needle after lifting the valve element from its seat in the opening direction. During the closing movement of the driver preferably remains in contact with the nozzle needle until it rests on its nozzle needle seat. This can, as already indicated, by a corresponding vote of at least two closing springs (nozzle needle closing spring and valve closing spring) can be achieved.

As already indicated, it is particularly preferred if a valve closing spring is provided for closing the valve. Preferably, in addition to the valve closing spring, a nozzle needle closing spring is provided for closing the nozzle needle. The spring forces of the valve closing spring and the nozzle needle closing spring are further preferably designed such that the nozzle needle reaches its closed position before the valve is closed and thus separates the pressure compensation chamber from the pressure region of the fuel injector.

Constructively advantageous is an embodiment in which in the nozzle needle a, preferably concentric to the longitudinal central axis extending, connecting channel is provided, can flow through the fuel with the valve open from the pressure range in the pressure compensation chamber. Preferably, this protrudes Valve element of the valve in the axial direction into the nozzle needle in order to close the connecting channel, preferably after closing the fuel injector can. Particularly preferably, the valve seat of the valve is for this purpose formed directly on the nozzle needle.

As indicated at the outset, an embodiment of the fuel injector is particularly preferred, in which the fuel injector is return connection connection-free, that is, neither a control amount nor a leakage quantity is obtained, which must be transported back into the fuel tank.

Although an embodiment of the fuel injector with piezo actuator is possible. For cost reasons, however, an embodiment is preferred in which the actuator for adjusting the nozzle needle and / or the valve is an electromagnetic actuator.

Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawings.

Fig. 1:

einen Kraftstoff-Injektor mit Druckausgleichsraum und einem diesen zugeordneten Ventil in einem geschlossen Zustand,

Fig. 2:

den Kraftstoff-Injektor gemäß Fig. 1 mit geöffnetem Ventil vor Beginn des Einspritzvorgangs,

Fig. 3:

den Kraftstoff-Injektor gemäß den Fig. 1 und 2 während des Einspritzvorgangs und

Fig. 4:

den Kraftstoff-Injektor gemäß den Fig. 1 bis 3 bei beendetem Einspritzvorgang jedoch bei noch geöffnetem Ventil.

These show in:

Fig. 1:

a fuel injector with pressure compensation chamber and a valve associated therewith in a closed state,

Fig. 2:

according to the fuel injector Fig. 1 with the valve open before starting the injection process,

3:

the fuel injector according to the Fig. 1 and 2 during the injection process and

4:

the fuel injector according to the Fig. 1 to 3 when the injection process is completed, however, with the valve still open.

In the figures, like elements and elements having the same function are denoted by the same reference numerals.

In Fig. 1 is a designed as a common-rail injector fuel injector 1 for injecting fuel into a combustion chamber, not shown also one not shown internal combustion engine shown. The fuel injector 1 is supplied, among other fuel injectors, not shown, via a supply line 2 with fuel under high pressure. In the case of forming the fuel injector as a diesel injector, this fuel pressure is preferably beyond 2000 bar. To generate the fuel pressure, a high-pressure pump 3 is provided, the fuel from a reservoir 4 (tank) in a high-pressure fuel storage 5 (Rail) conveys.

As it turned out Fig. 1 results, the fuel injector 1 only an inlet port 6, but not a return port.

Within a nozzle body 7, a nozzle needle 8 is guided axially adjustable. The nozzle needle 8 protrudes into a pressure region 9 (here pressure chamber 10), which is designed for reasons of vibration reduction as a mini-rail. In the pressure region 9, the supply line 2 opens, so that at least approximately rail pressure prevails in the pressure region 9, which in turn corresponds approximately to the injection pressure.

Fig. 1 shows the fuel injector 1 in the closed state. In this, the nozzle needle 8 is located with a cone-shaped sealing surface 11 on a nozzle needle seat 12 formed by a peripheral shoulder of the nozzle body 7. On the nozzle needle 8 acts in the plane of the drawing down, ie in the closing direction, a hydraulic closing force, which is due to the pressurization befindlichem in the pressure region 9, under pressure fuel.

To open the nozzle needle 8 and to open a valve 13 to be explained later, an actuator 14 designed as an electromagnetic actuator is provided, to which an anchor plate 15 is assigned. The anchor plate 15 is also located in the pressure region 9 of the fuel injector. 1

How to get out Fig. 1 shows, located in the plane of the drawing directly axially below the nozzle needle seat 12, an annular Ausmündungsbereich 16, from which a number of distributed over the circumference, introduced into the nozzle body 7 injection openings 17 open.

Axially in the plane of the drawing below, adjacent to the annular discharge area 16, which is hydraulically separated from the pressure area 9 in the closed state of the fuel injector 1, adjoins a guide section 18, in which the Nozzle needle 8 is guided on the inner circumference of a blind hole in the nozzle body 7. In the guide section 18, an annular gap seal 19 (guide gap) is formed radially between the nozzle needle 8 and the nozzle body 7. Axial to the annular gap seal 19 is adjacent in the drawing level below a pressure compensation chamber 20 at. This is at least largely decoupled hydraulically via the annular gap seal 19 of the Ausmündungsbereich 16. Via the valve 13, the pressure compensation chamber 20 can be connected to the pressure region 9, which is arranged on the side remote from the pressure compensation chamber 20 nozzle needle side. Since the diameter of the nozzle body 7 in the guide section 18 corresponds to the diameter of the nozzle needle seat 12, the nozzle needle 8 is pressure-balanced in the axial direction at pressure-compensating space 20 connected to the pressure region 9.

By a, preferably only slight, variation of the diameter of the nozzle needle seat 12 and the guide portion 18 and the annular gap seal 19, if necessary, a, preferably small, closing or opening pressure stage can be realized.

In the in Fig. 1 shown, fully closed state of the fuel injector 1 is both the nozzle needle 8 at its nozzle needle seat 12 and an axially adjustable valve element 21 of the valve 13 at its valve seat 22 at. The valve seat 22 is integrally formed on the nozzle needle 8. As long as the valve element 21 rests with its end face on the valve seat 22, no fuel from the pressure region 9 can flow through a centrally arranged in the nozzle needle 8 connecting channel 23 into the pressure compensation chamber 20, so that at least approximately combustion chamber pressure prevails in the pressure compensation chamber 20, so a (essential) lower pressure than in the pressure chamber 9.

Thus, the opening force of the (low-power) actuator 14 is sufficient to move the nozzle needle 8 from the illustrated closed position in an upward in the plane of the drawing open position, a hydraulic connection between the pressure region 9 and the pressure compensation chamber 20 must first be prepared. This is how it turns out Fig. 2 results, the actuator 14 energized. Due to the fixed connection between the armature plate 15 and the elongated valve member 21, the latter is moved in the drawing plane upwards, so that serving as a driver 24 circumferential collar 25 of the valve member 21 for axial abutment at a lower edge 26 of a through hole 27, the front side in the Nozzle needle 8 is introduced.

The passage opening 27 is penetrated in the axial direction by the valve element 21 - the driver 24 is thus trapped in an inner nozzle needle chamber 28.

As it turned out Fig. 2 results, first opens the valve 13 so that fuel from the pressure range 9 can first flow through a radial bore 29 into the nozzle needle chamber 28 and from this through the central connecting channel 23 in the axial direction down into the pressure compensation chamber 20. The connecting channel 23 is the only inlet and outlet opening of the pressure compensation chamber 20. From this open no injection openings. Due to the fuel flow from the pressure region 9 in the pressure compensation chamber 20 creates an acting in the opening direction hydraulic force completely compensated in the embodiment shown, the force acting in the closing direction hydraulic force, so that the nozzle needle 8 in the axial direction down only the spring force of a nozzle needle closing spring 30 acts, which is supported on the front side of the nozzle needle 8 and on the opposite side of a disc 31, which in turn is bolted to the nozzle body 7.

By the above-described mechanical coupling between the valve element 21 and the nozzle needle 8 via the driver 24, the nozzle needle 8 is entrained in a further axial displacement movement of the valve element 21 in the plane of the drawing upwards (see. Fig. 3 ), whereby a hydraulic connection between the pressure region 9 and the Ausmündungsbereich 16 is prepared so that fuel from the Ausmündungsbereich 16 and from the pressure region 9 can flow directly through the injection openings 17 into the combustion chamber of the internal combustion engine. To end the injection process, the energization of the actuator 14 is interrupted. As a result, the valve element 21 is moved downwards in the plane of the drawing by means of a valve closing spring 32, which is supported at one end on a peripheral collar 33 of the valve element 21 and the other end, and the spring force of the valve closing spring 32 is less than the spring force of the nozzle needle spring 30. so that the downward movement of the valve element 21 and the nozzle needle 8 is initially coupled, before the nozzle needle 8 reaches its respective closed position in front of the valve element 21. Due to the closing movement of the nozzle needle, as in Fig. 4 indicated by arrows, fuel displaced from the pressure compensation chamber 20. This displaced fuel flows back through the connecting channel 23 and the radial bore 29 in the pressure region 9. Supported by the spring force of the valve closing spring 32, the valve element 21 moves towards the valve seat 22 and closes the pressure compensation chamber 20 to prevent further leakage losses with the fuel injector closed from the pressure compensation chamber 20 via the annular gap seal 19 in the Ausmündungsbereich 16 and from there via the injection openings 17 into the combustion chamber. After closing the valve 13 is again in Fig. 1 shown state reached.

Claims (11)

1. Fuel injector for injecting fuel into a combustion chamber of an internal combustion engine, having a nozzle needle (8) which can be adjusted by means of an actuator (14) between a closed position and an open position which permits the flow of fuel from a pressure region (9) through at least one injection opening (17), characterized
   in that the pressure region (9) can be connected by means of a valve (13) to a pressure equalization chamber (20) which is delimited by the nozzle needle (8), wherein the pressure equalization chamber (20) and the pressure chamber (9) are arranged on mutually opposite sides of the nozzle needle (8), wherein the actuator (14) for adjusting the nozzle needle (8) serves simultaneously for adjusting a valve element (21) of the valve (13), and wherein the valve element (21) opens the connection between the pressure equalization chamber (20) and the pressure region (9) when in an open position and blocks said connection when in a closed position, a hydraulic closing force acting on the nozzle needle (8) in the closing direction being able to be at least partially compensated owing to the hydraulic connection.
2. Fuel injector according to Claim 1,
   characterized
   in that the pressure equalization chamber (20) is hydraulically separated from a mouth region (16) of the at least one injection opening (17), preferably from the entire injection opening (17), by means of an annular gap seal (19).
3. Fuel injector according to one of Claims 1 and 2, characterized
   in that the diameter of the annular gap seal (19) at least approximately corresponds to the diameter of a nozzle needle seat (12).
4. Fuel injector according to one of the preceding claims,
   characterized
   in that the valve (13) can be opened before the nozzle needle (8) is lifted out of its closed position.
5. Fuel injector according to one of the preceding claims,
   characterized
   in that the valve (13) can be closed after the nozzle needle (8) reaches the closed position.
6. Fuel injector according to Claim 1,
   characterized
   in that the valve element (21) is coupled in particular mechanically to the nozzle needle (8), preferably in such a way that an opening of the valve (13) leads to a time-offset adjustment of the nozzle needle (8) out of its closed position.
7. Fuel injector according to one of Claims 1 and 6, characterized
   in that a valve closing spring (32) is provided for closing the valve (13).
8. Fuel injector according to one of the preceding claims,
   characterized
   in that a nozzle needle closing spring (30) is provided for closing the nozzle needle (8).
9. Fuel injector according to one of the preceding claims,
   characterized
   in that, in the nozzle needle (8), there is provided a connecting duct (23) which runs preferably concentrically with respect to the longitudinal central axis of said nozzle needle and through which, when the valve (13) is open, fuel can flow from the pressure region (9) into the pressure equalization chamber (20).
10. Fuel injector according to one of the preceding claims,
    characterized
    in that the fuel injector (1) has no return connection.
11. Fuel injector according to one of the preceding claims,
    characterized
    in that the actuator (14) is an electromagnetic actuator (14).

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