WO2017032485A1

WO2017032485A1 - Actuator for a fuel injector, and fuel injector

Info

Publication number: WO2017032485A1
Application number: PCT/EP2016/064882
Authority: WO
Inventors: Georg Sengseis
Original assignee: Robert Bosch Gmbh
Priority date: 2015-08-21
Filing date: 2016-06-27
Publication date: 2017-03-02
Also published as: DE102015216032A1

Abstract

The invention relates to an actuator for a fuel injector, in particular a common rail injector, comprising a magnetic coil (1) surrounding an opening, wherein a piston (2) is inserted in the opening, which piston at least in some sections consists of a first magnetostrictive material, so the piston (2) experiences an elastic length change under the effect of a magnetic field produced by the magnetic coil (1). According to the invention, a pipe body (3) is arranged between the magnetic coil (1) and the piston (2), on which the piston (2) is supported in the axial direction, wherein the pipe body (3) at least in some sections consists of a second magnetostrictive material so that the pipe body (3) experiences an elastic length change parallel to the piston (2) under the effect of a magnetic field produced by the magnetic coil (1), wherein the magnetostrictive materials of the piston (2) and of the pipe body (3) behave in opposing manners under the effect of the magnetic field. The invention also relates to a fuel injector comprising such an actuator.

Description

Description title

Actuator for a fuel injector and fuel injector

The invention relates to an actuator for a fuel injector having the features of the preamble of claim 1. Furthermore, the invention relates to a fuel injector with such an actuator.

In conjunction with the fuel injector, the actuator is used to control the lifting movement of a nozzle needle in order to initiate and / or terminate an injection process.

State of the art

In fuel injectors predominantly electromagnetic or piezoelectric actuators are used. In addition, however, fuel injectors with magnetostrictive actuators are also known.

From the publication US 2014/0217932 AI, for example, a fuel injector with a magnetostrictive actuator shows that a rod from a

magnetostrictive material surrounded by a magnetic coil. When a magnetic field is generated across the magnetic coil, the magnetostrictive material expands, causing the rod to elongate. The elongation of the rod causes an axial displacement of a piston, which in turn is converted into a lifting movement of a nozzle needle.

By means of such magnetostrictive actuators, however, only relatively small strokes can be realized. Because the change in length of a body

magnetostrictive material is based on the effect that under the action of a Magnetic field changes the orientation of the magnetic domains. The volume of the body remains unchanged.

In order to realize sufficiently large strokes when using such an actuator in a fuel injector, a device for path translation can be provided. Alternatively or additionally, the body can be preloaded.

How the bias affects, is shown schematically in Figure 6. The bias of a magnetostrictive material body causes alignment of the magnetic domains transverse to the direction of elongation (a). By contrast, in the case of an unbiased body, the magnetic domains are not aligned (b). Under the influence of a magnetic field, the magnetic domains are aligned parallel to the direction of expansion (c), whereby the change in length Ali is greater than the change in length ΔΙ ₂ .

The change in length is elastic, d. h., that after the body contracts again when the magnetic field is degraded. The change in length does not necessarily cause an elongation of the body. Because magnetostrictive materials are also known which contract under the action of a magnetic field (see FIG. 7, which by way of example shows two oppositely acting magnetostrictive materials in a juxtaposition).

In order to achieve larger strokes, the body of magnetostrictive material can also be made larger. However, this has the consequence that the space requirement increases.

Based on the above-mentioned prior art, the present invention, the object of a magnetostrictive actuator for a

Specify Krafstoffinjektor that allows larger working strokes with approximately the same space requirement and approximately the same strength of the magnetic field compared to the known magnetostrictive actuators. Furthermore, the actuator should be suitable for direct control of the lifting movement of a nozzle needle in a fuel injector and in this way enable a return-quantity-free operation of the fuel injector. To achieve the object of the actuator with the features of claim 1 is given. Furthermore, a fuel injector is proposed with such an actuator. Advantageous developments of the invention are to be taken from the respective subclaims.

Disclosure of the invention

The actuator proposed for a fuel injector, in particular a common rail injector, comprises a magnetic coil enclosing an opening. In the opening, a piston is inserted, which at least partially from a first

magnetostrictive material, so that the piston undergoes an elastic change in length under the action of a magnetic field generated by the magnetic coil. According to the invention, a tubular body is arranged between the magnetic coil and the piston, on which the piston is supported in the axial direction. The tubular body consists at least in sections of a second magnetostrictive material, so that the tubular body undergoes an elastic change in length parallel to the piston under the action of a magnetic field generated by the magnetic coil. The magnetostrictive materials of the piston and the tube body behave in opposite directions under the influence of the magnetic field. That is, one body contracts while the other body expands.

The axial support of the piston on the tubular body causes a mechanical coupling of the two bodies. This in turn means that the changes in length of the two bodies add up. The change in length in total is greater than that of each individual body, so that in this way a larger working stroke with approximately the same space requirement, at least in the axial direction, and approximately the same strength of the magnetic field can be realized. Essential is the use of different magnetostrictive materials that behave contrary under the action of a magnetic field. For example, a magnetostrictive material that expands under exposure is terfenol-D. For example, samfenol-D behaves in the opposite direction, ie, samfenol-D contracts under the influence of a magnetic field. It is also essential that the bodies of different magnetostrictive materials are connected and coupled in parallel so that their length changes add up.

Preferably, the piston is cylindrical and the tubular body is designed as a hollow cylinder. The magnetic coil is furthermore preferably annular. This embodiment has the advantage that the angular position of the components is irrelevant to each other. However, this does not exclude that the abovementioned components can also have a cross-sectional shape deviating from a circular or annular cross-sectional shape, for example a quadrangular or polygonal cross-sectional shape.

Preferably, the piston consists at least in sections of a magnetostrictive material which contracts under the action of a magnetic field. This material may be, for example, Samfenol-D. The tube body in this case consists of a magnetostrictive material which expands under the action of a magnetic field, such as terfenol-D. This combination of materials has the advantage that the actuator can be installed in the manner in a fuel injector, that the direction of movement of the piston when contracting the direction of movement of the nozzle needle corresponds. Accordingly, no means for reversing direction must be provided. Concrete embodiments will be described in more detail below in connection with a fuel injector according to the invention.

Furthermore, the piston preferably has at least one end section which projects beyond the magnet coil and / or the tubular body in the axial direction. This embodiment of the piston facilitates on the one hand the axial support on the tubular body, preferably via a first end portion, which projects beyond the tubular body in the axial direction at least. On the other hand, the piston can be more easily coupled to the nozzle needle, wherein preferably the coupling takes place via a second end portion of the piston, which projects beyond the tube body and the magnetic coil in the axial direction.

Advantageously, the piston is axially biased by the spring force of a spring against the tubular body. The spring ensures that the axial support of the piston is maintained on the pipe body, even if, after removal of the Magnetic field of the piston and the tube body again assume their respective output form. At the same time, the spring causes an axial bias of the tubular body, whereby the magnetostrictive effect - as described above - is still increased. For this purpose, the tubular body is preferably supported on the housing side at its end facing away from the spring. This means that the change in length, in particular elongation, of the tubular body takes place counter to the spring force of the spring. In this case, the tubular body carries the piston, so that adds to the change in length of the piston, the change in length of the tubular body.

The provided for the axial bias of the piston relative to the tubular body spring is preferably on the one hand housing side and on the other hand supported on a support surface which is formed on the piston or on a fixedly connected to the piston body. For example, the piston for forming the support surface having a collar portion, in the region of which he has an enlarged outer diameter. About the collar portion of the piston can be axially supported at the same time on the tubular body.

The spring is preferably designed as a helical compression spring and pushed onto the piston, so that it further preferably surrounds an adjoining the collar portion end portion of the piston. In this way, on the one hand, a particularly compact construction in the axial direction is achieved. On the other hand, a guide of the spring can be effected via the piston.

In a further development of the invention it is proposed that the piston is axially biased by means of the spring force of another spring, namely a piston biasing spring. The axial bias causes the magnetostrictive effect is enhanced and the piston experiences a greater change in length under the action of a magnetic field. If the piston consists, at least in sections, of a magnetostrictive material which contracts under the action of a magnetic field, the prestressing of the piston takes place in the direction of elongation. That is, the piston is stretched by the biasing force.

Since the magnetostrictive materials of the piston and the tube body behave contrary under the action of a magnetic field, the same applies analogously to the axial Preloading the body to enhance the magnetostrictive effect. That is, upon expansion of the piston by the piston bias spring, the tube body is compressed by the biasing force of the other spring. It is also proposed that the piston biasing spring on the one hand the housing side and on the other hand supported on a support surface which is formed on the piston or on a fixedly connected to the piston body. For example, the support surface may be formed on a collar portion of the piston. The piston biasing spring may be formed as a helical compression spring and pushed onto the piston so that it surrounds a portion of the piston. On the one hand, an arrangement which is particularly compact in the axial direction is achieved in this way, on the other hand a guidance of the spring can be effected via the piston.

Advantageously, the piston is composed of several parts. The multi-part design allows the use of different materials, so that an optimal matching of the material to the respective function of a part can take place. For example, at least one end portion of the piston can be made of a particularly wear-resistant material in order to increase the robustness of a stop, contact and / or guide surface formed thereon. Furthermore, the multi-part design of the piston simplifies the assembly of the actuator. This is especially true when the piston has in the region of its two ends a radially outwardly extending collar portion for forming a support surface. For then serving to form a collar portion can be connected only after the onset of the piston in the tubular body with the piston. The connection of the several parts of the piston can be effected, for example, via a plug-in, press, screw, adhesive and / or welded connection.

Since the advantages of an actuator according to the invention come into play, in particular when used in a fuel injector, a fuel injector for injecting fuel into a combustion chamber of an internal combustion engine with a fuel injector is also provided

Actuator proposed. The actuator is used to actuate a nozzle needle, which is received in a liftable manner for releasing and closing at least one injection opening in a high-pressure bore of a nozzle body. Preferably, the nozzle needle via the actuator is directly actuated. This means that - in contrast to the indirect Control via a control valve - no Absteuermenge accumulates, which must be supplied to a return. A direct actuation of the nozzle needle is possible because comparatively large working strokes can be realized via the actuator according to the invention.

Preferably, the nozzle needle and the piston of the actuator are hydraulically coupled via a coupler volume. The hydraulic coupling has the advantage that in a simple way, a force or displacement translation can be realized by the area ratio of the formed on the nozzle needle and the piston hydraulic active surfaces for limiting the coupler volume is selected accordingly. A force or displacement transmission effected in this way can be used as a support.

Further preferably, the coupler volume for the hydraulic coupling of the nozzle needle and the piston is divided into two coupler spaces, which are hydraulically connected via a connecting channel. The connecting channel is preferably formed in an intermediate plate between the nozzle body and a

Injector body of the fuel injector is arranged, in which the actuator is accommodated. The separation of the coupler volume into two coupler spaces facilitates the compensation of any axis errors between the longitudinal axis of the nozzle needle and the longitudinal axis of the piston. This applies in particular if, for the radial delimitation of the coupler spaces, in each case one sealing sleeve axially supported on the intermediate plate is provided in which an end section of the nozzle needle or of the piston is received in a liftable manner.

As a further development measure, it is proposed that an end section of the piston is received in a guide bore of a holding body of the fuel injector. About the guide bore a guide of the piston is effected in a simple manner. The radial clearance between the piston, the tubular body and the solenoid can therefore be chosen sufficiently large to ensure the desired length changes. In addition, it is proposed that the end portion of the piston within the guide bore limits a volume which is hydraulically connected via at least one throttle bore to a high-pressure region. The volume can be used in this case to dampen or compensate for any natural oscillations of the piston in a change in length. Preferred embodiments of the invention are explained below with reference to the accompanying drawings. These show:

1 shows a schematic longitudinal section through an actuator according to the invention according to a first preferred embodiment,

2 shows a schematic longitudinal section through an actuator according to the invention according to a second preferred embodiment, FIG. 3 shows a schematic longitudinal section through a fuel injector according to the invention with an actuator according to FIG. 2, FIG.

4 shows a schematic longitudinal section through an actuator according to the invention according to a third preferred embodiment,

5 shows a schematic longitudinal section through a fuel injector according to the invention with an actuator according to FIG. 4, FIG.

Fig. 6 is a schematic representation of the orientation of the magnetic domains in a magnetostrictive material and

7 shows a diagram to illustrate the changes in length of magnetostrictive materials which behave in a contradictory manner under the action of a magnetic field. Detailed description of the drawings

The actuator shown in Fig. 1 comprises an annular magnetic coil 1 for acting on a piston 2, which consists of a first magnetostrictive material. The piston 2 is partially surrounded by a tubular body 3, which consists of a second magnetostrictive material. The first and the second magnetostrictive material behave in opposite directions under the action of a magnetic field, with the material of the piston 2 contracting and that of the tubular body 3 expanding (see arrows in FIG. 1). If the magnetic coil 1 is energized, forms a force acting on the tube body 3 and the piston 2 magnetic field. This has the consequence that the tubular body 3 expands (arrow 24) and the piston 2 contracts (arrow 25). Since the piston 2 is supported in the axial direction on the tubular body 3, the elongation of the tubular body 3 leads to an increase of the piston 2. At the same time, the piston 2 contracts. Both length changes add up to a sum movement (arrow 26), which corresponds to the working stroke of the actuator.

The changes in length of the tubular body 3 and the piston 2 are elastic. This means that after removal of the magnetic field both bodies resume their original form. In order to ensure in the provision that the piston 2 and the tubular body 3 remain mechanically coupled, a spring 4 is provided which biases the piston 2 axially against the tubular body 3. The spring 4 designed as a helical compression spring is supported on the housing side on a holding body 20, on the other hand on an annular support surface 5, which is formed on a collar portion of the piston 2, via which the piston 2 is also axially supported on the tubular body 3. The support surface 5 may also be formed on a body 22 which is fixedly connected to the piston 2 (see reference numerals in parentheses). The spring 4 is penetrated by an end portion 2.1 of the piston 2, the end in a Führungsbor- hung 32 of the holding body 20 is liftably received and guided. In this case, the end section 2.1 of the piston 2 defines a formed within the guide bore 32 volume 34, which communicates via throttle bores 33 in communication with a high-pressure region 35 of the fuel injector. By way of the volume 34, an attenuation of the piston 2 is simultaneously effected in this way, which minimizes natural vibrations. The leadership of the spring 4 is effected via the piston 2.

About the collar portion of the piston 2 and the body 22 supported spring 4 and the tube body 3 is axially biased. The axial bias causes a compression of the tubular body 3. This has the consequence that under the action of a magnetic field, the magnetostrictive effect is enhanced.

In order to further enhance the magnetostrictive effect, a piston biasing spring 6 is further provided for axially biasing the piston 2. However, the spring force of the piston pretensioning spring 6, which is likewise designed as a helical compression spring, causes a ne expansion of the piston 2. The piston biasing spring 6 is for this purpose on the one hand housing side, namely on an injector body 19, on the other hand supported on an annular support surface 7 of the piston 2. The annular support surface 7 may in turn be formed on a collar portion of the piston 2 or on a body 23 which is fixedly connected to the piston 2 in the region of a further end portion (2.2)

(see reference numerals in parentheses).

FIG. 2 shows a further preferred embodiment of an actuator according to the invention. In this embodiment, only one spring 4 is provided, which biases the piston 2 axially against the tubular body 3. On an additional

Piston biasing spring 6 has been omitted. In addition, the piston 2 at its end facing away from the spring 4 a modified end portion 2.2. This has an enlarged compared to the other piston 2 outer diameter, which is suitable in particular for hydraulic coupling with a nozzle needle 8 of a fuel injector. The end portion 2.2 can by the piston 2 itself or by one with the

Piston 2 firmly connected body 23 (see reference numerals in brackets) are formed.

FIG. 3 shows, for example, a fuel injector with an actuator according to FIG. 2. The actuator is accommodated in an injector body 19 in which a laterally

Inlet channel 21 is formed. The injector body 19 is connected via an intermediate plate 18 with a nozzle body 11, in which a high-pressure bore 10 is formed, which is supplied via the inlet channel 21 with fuel. In the high-pressure bore 10, the nozzle needle 8 is received, via the lifting movement Einspritzöff- openings 9 are releasable or closed. The actuator is used to control the lifting movement of the nozzle needle. 8

To control the lifting movement of the nozzle needle 8, the piston 2 of the actuator and the nozzle needle 8 are hydraulically coupled via a coupler volume 12. The intermediate plate 18 divides the coupler volume 12 into an upper and a lower one

Coupler space 15, 16, which are connected via a connecting channel 17. The upper coupler space 16 is bounded by a hydraulic active surface 14 of the piston 2. The boundary of the lower coupler space 15 is effected by a formed on the nozzle needle 8 hydraulic active surface 13. The area ratio of the hydraulic see active surfaces 13, 14 is selected such that on the hydraulic coupling at the same time a force or Wegverstärkung is achieved. In the radial direction both coupler spaces 15, 16 each bounded by a sealing sleeve 27, 28 which is supported on the intermediate plate 18 and axially biased by the spring force of a spring 29, 30 against the intermediate plate 18.

A further preferred embodiment of an actuator according to the invention is shown in FIG. 4. This differs from that of FIG. 2 in that the piston 2 is designed in several parts.

In FIG. 4, the piston 2 comprises three parts, namely the actual piston 2 and the bodies 22, 23, which are firmly connected to the piston 2. The body 23 has a collar 31 for supporting the spring 30, whose spring force acts on the sealing sleeve 28 in the direction of the intermediate plate 18. In order to increase the robustness of the piston 2 in the region of the body 23, the body 23 is formed of a material that is not magnetostrictive, but particularly wear-resistant.

FIG. 5 shows a fuel injector with an actuator according to FIG. 4. As can be seen from FIG. 5, the body 22 may also be made of a material which is not magnetostrictive but particularly resistant to wear.

FIGS. 6 and 7 have already been explained in the introduction, so that further explanations are unnecessary for this purpose.

Claims

claims

1. Actuator for a fuel injector, in particular a common rail injector, comprising a magnetic coil enclosing an opening (1), wherein in the opening a piston (2) is inserted, at least partially from a first

magnetostrictive material, so that the piston (2) undergoes an elastic change in length under the action of a magnetic coil (1) generated magnetic field, characterized in that between the magnetic coil (1) and the piston (2) a tubular body (3) is arranged , on which the piston (2) is supported in the axial direction, wherein the tubular body (3) at least partially from a second

magnetostrictive material, so that the tube body (3) under the action of a magnetic coil (1) generated magnetic field undergoes an elastic change in length parallel to the piston (2), wherein the magnetostrictive materials of the piston (2) and the tubular body (3) below The action of the magnetic field behaves contrary.

2. Actuator according to claim 1,

characterized in that the magnetostrictive material of the piston (2) contracts under the action of a magnetic field and the magnetostrictive material of the tubular body (3) expands under the action of a magnetic field.

3. Actuator according to claim 1 or 2,

characterized in that the piston (2) has at least one end portion (2.1, 2.2), which projects beyond the magnetic coil (1) and / or the tubular body (3) in the axial direction.

4. Actuator according to one of the preceding claims,

characterized in that the piston (2) by means of the spring force of a spring (4) is axially biased against the tubular body (3), wherein preferably the spring (4) on the one hand housing side and on the other hand supported on a support surface (5) on the piston ( 2) or on a with the piston (2) fixedly connected body (22) is formed.

5. Actuator according to one of the preceding claims,

characterized in that the piston (2) by means of the spring force of a piston biasing spring (6) is axially biased, wherein preferably the piston biasing spring (6) on the one hand housing side and on the other hand on a support surface (7) is supported on the piston (2) or on a is formed with the piston (2) fixedly connected body (23).

6. Actuator according to one of the preceding claims,

characterized in that the piston (2) is composed of several parts.

7. Fuel injector for injecting fuel into a combustion chamber (1) of an internal combustion engine, comprising an actuator according to one of the preceding claims for actuating a nozzle needle (8) for releasing and closing at least one injection opening (9) in a high-pressure bore (10) of a Nozzle body (11) is received in a liftable manner.

8. Fuel injector according to claim 7,

characterized in that the nozzle needle (8) and the piston (2) of the actuator via a coupler volume (12) are hydraulically coupled, wherein preferably the area ratio of the at the nozzle needle (8) and the piston (2) formed hydraulic active surfaces (13, 14) for limiting the coupler volume (12) is selected such that a force or displacement transmission is effected.

9. Fuel injector according to claim 8,

characterized in that the coupler volume (12) is subdivided into two coupler spaces (15, 16) which are hydraulically connected via a connecting channel (17), wherein preferably the connecting channel (17) is formed in an intermediate plate (18) interposed between the coupler Nozzle body (11) and an injector body (19) is arranged, in which the actuator is accommodated.

10. Fuel injector according to one of claims 7 to 9,

characterized in that an end portion (2.1) of the piston (2) in a guide bore (32) of a holding body (20) is received, wherein preferably the end portion (2.1) defines a volume (34) within the guide bore (32), over at least one throttle bore (33) is hydraulically connected to a high-pressure region (35).