EP2204571A1 - Fuel injector with piezoelectric actuator - Google Patents

Abstract

The injector (1) has a piezoelectric actuator (24), and a hydraulic coupler (25) attached to the actuator and including a coupler piston (27) actuated by the piezoelectric actuator. A working piston (28) is coupled with the coupler piston over a coupler gap volume. The coupler gap volume is filled by a check valve, which has an adjustable valve element cooperating with a valve seat. The valve element has an even surface section on its side turned away from the valve seat. The valve element cooperates with a ball section with the valve seat.

Description

State of the art

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

Fuel injectors are known with a piezoelectric actuator for actuating a control valve, wherein the piezoelectric actuator via a hydraulic coupler, comprising a coupler piston and a working piston, is coupled to the control valve element. Upon actuation of the hydraulic coupler by means of the piezoelectric actuator occurs via guide games between the piston and a guide body to an unavoidable leakage. The refilling of the coupler volume also takes place via these guide games. A disadvantage of such fuel injectors is that it can lead to an idling of the coupler volume and thus to a failure of the fuel injector. This is due to the fact that for very long or many short switching times, the leakage from the coupler volume is greater than the re-filling, since the refilling takes place at a much lower pressure difference.

From the DE 100 37 527 A1 It is known to refill the Kopplerspaltvolumen of the hydraulic coupler via a check valve, wherein the actuated by a valve spring, spherical valve element of the check valve is located in a frontal recess of the force acting on the control valve member working piston. The valve spring of the check valve tends to move away from each other the coupler piston coupled to the piezoelectric actuator and the working piston. The well-known fuel injector shines in In view of minimizing the switching time as in terms of achieving a precise switching game in need of improvement.

The DE 197 38 351 A1 shows a fuel injector with an electromagnetic actuator with which a kugelkalottenförmiges control valve element is axially actuated. The known fuel injector is not suitable for switching pressures beyond 2000bar.

Disclosure of the invention

The invention has for its object to optimize a fuel injector with piezoelectric actuator and hydraulic coupler with a view to improved refilling at an increased number of injections per stroke. From this follows an optimization of the switching time as well as an increased number of switching cycles.

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 has recognized that the switching time of the fuel injector can be improved if the dead volume of the check valve serving to replenish the volume of the coupler is minimized. To minimize the dead volume and thus to minimize the switching time, the invention proposes to deviate from a spherical shape of the valve element, so as to be able to minimize the valve element receiving, essentially determining the dead volume valve chamber of the check valve. In order to achieve a more precise switching cycle in addition to a reduction of the dead volume, the invention proposes at the same time to provide on the valve element a flat surface portion (flat portion), which is preferably arranged such that the fuel from the coupler volume for closing (kickback) of the check valve perpendicular to press the plane surface section. In other words, by providing a flat surface section, the switching cycle can be reduced and, secondly, the switching time can be reduced. It is the Reduction of the switching time essentially due to the reduction of the dead volume, which in turn leads to an increase in rigidity of the entire hydraulic coupler (coupler module). Overall, there is thus an improvement in the entire hydraulic coupler behavior. The inventive construction of the valve element of the check valve allows a particularly preferred embodiment of the check valve, in which this manages without valve spring. In other words, an embodiment is particularly preferred in which the check valve is designed to be free of valve spring for refilling the coupler volume. As a result, the dead volume can be further reduced and the maximum displacement of the valve element can be reduced to a minimum.

As already indicated, it is advantageously provided in a development of the invention that the planar surface section of the valve element is oriented perpendicular to the adjustment direction of the valve element so that the fuel pressing against the valve element when the piezoelectric actuator is energized receives a large-area attack surface. In addition, such an arrangement of the flat surface portion on the side facing away from the valve seat of the check valve side provides a support for the valve element of the check valve in the open state.

Very particularly preferred is an embodiment in which the valve element has a spherical section adjacent to the planar surface section, i. is formed in the manner of a spherical cap or has a partial spherical shape. Preferably, only the ball portion and not the flat surface portion cooperates with the valve seat of the check valve to close the same.

An embodiment of the fuel injector in which the coupler gap volume is refilled exclusively via the low-pressure region of the fuel injector is very particularly preferred. For this purpose, the check valve in the opened state connects the low-pressure region of the fuel injector with the coupler gap volume. Most preferably, the piezoelectric actuator is located in the low pressure region of the fuel injector connected to an injector return port.

In a further development of the invention is advantageously provided that the check valve is not arranged in the working piston of the hydraulic coupler, but in the directly operatively connected to the piezoelectric actuator coupler piston. Such an embodiment is structurally particularly preferred in order to easily provide a Rückbefüllmöglichkeit the Kopplervolumens from the low pressure region of the fuel injector.

Particularly useful is an embodiment in which is connected via a provided in the coupler piston axial channel and the axial channel perpendicularly impinging radial passage with the low pressure region of the fuel injector. Most preferably, the axial channel is a central, arranged coaxially to the longitudinal central axis of the coupler piston channel. The radial channel is preferably realized as a through-channel, which supplies the axial channel from two opposite sides with fuel from the low-pressure region for refilling the coupler volume.

Particularly preferably, the possible travel of the valve element is limited to a minimum value range, preferably between about 0.08 mm and about 0.50 mm, whereby the switching cycle is further reduced. Ideally, the check valve is formed here valve spring free.

In a further development of the invention is advantageously provided that the, in particular dome-shaped valve element of the check valve is accommodated in an end-side recess of the coupler piston and held there by means of a recess closing Einpresselementes, such that it is within the recess, preferably axially between an open position and a closed position is adjustable.

In order to allow a fuel inlet from the recess closed by the press-in element into the actual coupler volume, at least one fuel channel is advantageously provided in the press-in element and / or radially between the press-in element and the inner circumference of the recess. Preferably, two parallel fuel channels are realized. More preferably, the two parallel fuel channels are axial bores in the press-in element.

In principle, the fuel injector can be a fuel injector in which the working piston forms the one-piece injection valve element or a part of the multipart injection valve element for closing and releasing at least one injection opening. Most preferably, however, it is a fuel injector with servo circuit, in which by means of the hydraulic coupler, a control valve (servo valve) is operable to connect a limited of the one- or multi-part injection valve element control chamber with a low pressure region of the fuel injector. In this case, the control valve element of the control valve can be formed either directly from the working piston of the hydraulic coupler or by means of the working piston operable by this separate component.

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

Fig. 1:

einen Common-Rail-Injektor mit piezoelektrischem Aktuator und hydraulischem Koppler,

Fig. 2:

eine vergrößerte Darstellung des hydraulischen Kopplers sowie eines Steuerventilelementes des Common-Rail-Injektors gemäß Fig. 1, und

Fig. 3:

eine vergrößerte Darstellung eines Details des hydraulischen Kopplers gemäß den Fig. 1 und 2.

These show in:

Fig. 1:

a common rail injector with piezoelectric actuator and hydraulic coupler,

Fig. 2:

an enlarged view of the hydraulic coupler and a control valve element of the common rail injector according to Fig. 1 , and

3:

an enlarged view of a detail of the hydraulic coupler according to the Fig. 1 and 2 ,

In the figures, the same components and components with the same function with the same reference numerals.

In Fig.1 is a trained as a common rail injector fuel injector 1 for injecting fuel into a combustion chamber, not shown, also shown an internal combustion engine of a motor vehicle. A high-pressure pump 2 conveys fuel from a reservoir 3 into a high-pressure fuel accumulator 4 (rail). In this fuel, especially diesel, under high pressure, stored in this embodiment about 2000bar. To the high-pressure fuel accumulator 4, the fuel injector 1, among other, not shown, fuel injectors 1, connected via a supply line 5. The supply line 5 opens into an axial supply channel 6 belonging to the high-pressure region of the fuel injector 1, through which fuel flows into a pressure chamber 7. During an injection process, the fuel flows from the pressure chamber 7 in the axial direction past a one-part injection valve element 8 (nozzle needle) through nozzle bores of a nozzle hole arrangement 16 into the combustion chamber of the internal combustion engine. The fuel injector 1 is connected via an injector return port 9 to a return line 10. Via the return line 10, a later to be explained control amount of fuel flow from the fuel injector 1 to the reservoir 3 and are fed from there from the high pressure circuit again.

As it turned out Fig. 1 results, the one-piece injection valve element 8 is guided axially adjustable within a stepped bore 11 of a nozzle body 12 in this embodiment. The nozzle body 12 is braced in connection with a throttle plate and a valve body against a holding body 13 by means of a nozzle retaining nut. The nozzle retaining nut is sealed by means of a copper disk in the direction of the combustion chamber into which projects the nozzle body tip.

The injection valve element 8 has at its tip 15 a closing surface (sealing surface), with which the injection valve element 8 can be brought into a tight contact with an injection valve element seat formed inside the nozzle body 12. When the injection valve member 8 abuts its injection valve member seat, i. is in a closed position, the fuel outlet from a nozzle hole arrangement 16 is locked. If, on the other hand, it is lifted from its injection valve element seat, fuel from the pressure chamber 7, substantially under rail pressure, can flow past the injection valve element seat into the combustion chamber.

From a drawing in the upper surface of the injection valve element 8 a control chamber 17 (servo chamber) is limited, which has a in the Fig. 2 indicated inlet throttle 18 is supplied with high-pressure fuel from the supply channel 6. At the same time, a pressure chamber 14, from which fuel can flow into the combustion chamber when the injection valve element 8 is open, is supplied with fuel from the supply channel 6. The pressure room 14 encloses a control chamber 17 limiting, spring-loaded sleeve 32 radially outward. The formed in the sleeve 32 control chamber 17 is connected via an outlet throttle 19 with a control valve chamber 20 which is connected by means of an axially adjustable control valve element 21 (valve pin) with a low pressure region 22 and thus with the injector return port 9. The control valve element 21 is part of a designed as a 3/2-way valve control valve 23 (servo valve). In a control valve element 21 located in a first (lower) switching position, fuel can flow from the control chamber 17 via the outlet throttle 19 and the control valve chamber 20 into the low-pressure region 22 to the injector return port 9. At the same time, a bypass 45 opening out of the pressure chamber 14 and opening into the control valve chamber 20 is blocked by the control valve element 21. When in a second (upper) switching position befindliches control valve element 21, the connection between the control valve chamber 20 and the low pressure region 22 is disabled and the bypass 45 is released, so that the control chamber 17 via the bypass 45, the control valve chamber 20 and the outlet throttle 19 is brought quickly to high pressure ,

For adjusting the piston-shaped control valve element 21, a piezoelectric actuator 24 is provided, which is coupled via a hydraulic coupler 25 to the control valve element 21. In an alternative embodiment, not shown, the control valve 23 may be formed directly by the hydraulic coupler 25, more specifically by a working piston 28 (valve piston) of the hydraulic coupler 25 to be explained later. To open the control valve 23, so moving the control valve element 21 in the plane of the drawing down, away from its upper control valve seat 26, the piezoelectric actuator 24 is energized and expands. As a result, an upper plane in the plane of the coupler piston 27 of the hydraulic coupler 25 is moved in the drawing plane down, which in turn the working piston 28 of the hydraulic coupler 25, which is hydraulically coupled via a Kopplerspaltvolumen 29 with the coupler piston 27 is moved in the drawing plane down , The working piston 28 presses on the control valve element 21 which is subsequently moved away from its upper control valve seat 26 against the force of a control closing spring 30 (switching valve spring) and thus releases the fuel flow from the control chamber 17 to the injector return port 9 and at the same time the bypass 45 locks. The flow cross sections of the inlet throttle 18 and the outlet throttle 19 are matched to one another such that in the lower switching position of the control valve 23, a net outflow of fuel from the control chamber 17 results. As a result, the pressure in the control chamber 17 decreases rapidly, whereby the injection valve element 8 lifts off from its injection valve element seat, so that fuel can flow out of the pressure chamber 7 through the nozzle hole arrangement 16.

To terminate the injection process, the energization of the piezoelectric actuator 24 is interrupted, whereby the piezocrystal stack of the actuator 24 contracts and the coupler piston 27, supported by the spring force of a spring sleeve 34, is moved in the drawing plane upwards. The working piston 28 presses, supported by the control closing spring 30, in the drawing plane down against the control valve element 21. Between the working piston 28 and the control valve element 21 thus a continuous contact is ensured. The working piston 28 and the control valve element 21 are moved at not energized actuator 24 upwards into the upper switching position in which the control valve element 21 rests again on its upper control valve seat 26 and the hydraulic connection from the control chamber 17 to the injector return port 9 blocks. The fuel flowing in through the inlet throttle 18 and via the bypass 45 into the control chamber 17 ensures rapid pressure increase in the control chamber 17 and thus for a hydraulic closing force acting on the injection valve element 8. The resulting closing movement of the injection valve element 8 is assisted by a closing spring 31, which is supported with one end on the injection valve element 8 and with the other end on a control chamber 17 limiting sleeve 32.

Hereinafter, the structure of the hydraulic coupler 25 based on the Fig. 2 and 3 explained in detail. Evident is the directly connected to the piezoelectric actuator 24, in the plane of the upper coupler piston 27 and the drawing plane in the lower, spaced-apart piston 28. Kopplerkolben 27 and piston 28 axially delimit between them within a guide body 33, a hydraulic Kopplerspaltvolumen 29 (fuel volume ). It can be seen that the diameter of the working piston 28 is dimensioned smaller than the diameter of the coupler piston 27, thereby realizing a force-displacement ratio.

As it turned out Fig. 3 further results, a check valve 35 is disposed within the coupler piston 27. The check valve 35 serves to refill the Kopplerspaltvolumens 29 after interruption of the energization of the piezoelectric actuator. The check valve 35 is formed valve spring-free and comprises a kugelkalottenförmiges valve element 36 which is received in an end-side recess 37 of the coupler piston 27. The recess 37, which is originally open in the direction of the working piston 28, is closed by means of a press-in element 38 (press-in disk), wherein the press-in element 38 limits the maximum axial adjustment path of the valve element 36. How to get out Fig. 3 shows, in the press-in element 38 two parallel axial bores 39 (fuel channels) introduced, can flow through the fuel with open check valve 35 to a central axial passage 40 in the Kopplerspaltvolumen 29. The axial channel 40 is cut perpendicularly by a transverse, designed as a through-bore radial passage 41, which connects the check valve 35 hydraulically with the aforementioned low-pressure region 22 of the fuel injector 1.

As it turned out Fig. 3 results further, the valve element 36 is substantially hemispherical in shape and has a plane in the plane of the upper ball portion 42 for cooperation with a valve seat 43. With a flat surface portion 44 facing away from the valve seat 43, the valve element 36 can be supported on the press-in element 38 when the check valve 35 is open, such that a force entry into the coupler gap volume 29 through the axial bores 39 is possible. By providing the check valve 35, a fast refilling of the coupler gap volume 29 is ensured. The coupler gap volume 29 does not have to be (exclusively) via guide plays between the coupler piston 27 and / or the working piston 28 and the guide body 33.

Claims (10)

A fuel injector, in particular a common rail injector, for injecting fuel into a combustion chamber of an internal combustion engine, having a piezoelectric actuator (24) and a hydraulic coupler (25) associated therewith, comprising a coupler piston actuable by means of the piezoelectric actuator (24) ( 27) and one with the coupler piston (27) via a Kopplerspaltvolumen (29) coupled to the working piston (28), wherein the Kopplerspaltvolumen (29) via a check valve (35) can be filled, which an adjustable, with a valve seat (43) cooperating valve element ( 36),
characterized,
side of the valve element (36) on its side remote from the valve seat (43) has a flat surface portion (44). Fuel injector according to claim 1,
characterized,
that the flat surface portion (44) is oriented perpendicular to the adjustment direction of the valve element (36). Fuel injector according to one of claims 1 or 2,
characterized,
in that the valve element (36) cooperates with a ball section (42) with the valve seat (43). Fuel injector according to one of the preceding claims,
characterized,
in that the coupler gap volume (29) can be connected via the check valve (35) to a low-pressure region (22) of the fuel injector (1). Fuel injector according to one of the preceding claims,
characterized,
in that the check valve (35) is arranged in the coupler piston (27). Fuel injector according to claim 5,
characterized,
in that the non-return valve (35) is connected to the low-pressure region (22) of the fuel injector (1) via an axial channel (40) provided in the coupler piston (27) and in particular a radial channel (41). Fuel injector according to one of the preceding claims,
characterized,
that the maximum displacement of the valve element (36) is selected from a range between about 0.08 mm and about 0.50 mm. Fuel injector according to one of the preceding claims,
characterized,
that the valve element (36) is received in an end recess (37) of the coupler (27) and is held there by means of adjustable Einpresselementes (38). Fuel injector according to claim 8,
characterized,
in that at least one fuel channel is provided in the press-fit element (38) and / or radially between the press-fit element (38) and the inner circumference of the end-side recess (37), via which fuel can flow into the coupler gap volume (29) when the check valve (35) is open. Fuel injector according to one of the preceding claims,
characterized,
in that a control valve (23) can be actuated by means of the hydraulic coupler (25), with which a control chamber (17) delimited by a one-piece or multi-part injection valve element (8) can be connected to a low-pressure region (22) of the fuel injector (1).

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