WO2005108774A1

WO2005108774A1 - Fuel injector featuring corrigible adjustment of an empty stroke of an actuator unit

Info

Publication number: WO2005108774A1
Application number: PCT/EP2005/052101
Authority: WO
Inventors: Wolfgang Guglielmi; Jens Linke; Ronald Reichel; Bernd Schaffert
Original assignee: Siemens Aktiengesellschaft
Priority date: 2004-05-10
Filing date: 2005-05-10
Publication date: 2005-11-17
Also published as: DE102004022958A1

Abstract

The invention relates to fuel injectors which are embodied especially with a piezoelectric actuator unit (12) as a driving mechanism and in which an empty stroke having a small gap size (s) generally has to be provided between the actuator unit (12) and a nozzle unit (15) in order to compensate temperature-related influences during operation of the fuel injector (10) as well as component tolerances. It is extremely difficult, however, to adjust a small gap size (s) with precision when serially producing fuel injectors. Said difficulty can be overcome by a fuel injector (10) in which the gap size (s) is adjusted by simply tightening a nozzle-clamping nut (17), wherefore the injector housing (11) and/or the nozzle housing (16) is/are made of a compressible steel material such that the fuel injector (10) can be shortened slightly when tightening the nozzle-clamping nut (17). The inventive fuel injector (10) has the advantage of dispensing with the need for an elastic intermediate ring while component tolerances are automatically compensated and the adjustment is reversible and easy to make.

Description

description

Fuel injector with a correctable setting of an empty stroke of an actuator unit

According to the preamble of the main claim, the invention is based on a fuel injector with an injector housing which is connected to a nozzle housing by means of a nozzle clamping nut by means of a releasable screw connection. An actuator unit is arranged in the interior of the injector housing in such a way that its upper end face is firmly connected to the injector housing. The lower end face of the actuator unit is movably arranged and expands axially downwards when a DC voltage is applied. In the nozzle housing arranged below there is a nozzle unit which is arranged with a predetermined gap to the actuator unit. The gap dimension corresponds to an idle stroke of the actuator unit. In this fuel injector, when the actuator unit is actuated, an idle stroke formed by the gap must first be overcome before the actuator unit can expand further to switch the nozzle unit.

It has been shown that the exact setting of the gap dimension is extremely difficult and complex, especially in series production, especially since the individual assemblies can only be manufactured in the fuel injector with a certain tolerance measure. In order to solve this problem, intermediate washers with different tolerance dimensions have already been manufactured. Each individual fuel injector must then be measured precisely and then a suitable washer selected and individually installed. This complex process is less suitable for series production.

From DE 19832826 AI is an assembly method for a

Fuel injection valve is known, with which a gap dimension or an idle stroke can be set. To be there- Injection valve comprises two housing parts, the first housing part being designed as a trough into which the second housing part can be screwed up to a desired position. A valve closing member is arranged in the tub. It should be installed in such a way that it takes up the predetermined gap dimension for an armature plate of a magnet armature core embedded in the second housing part. A deformable intermediate ring is arranged between the two housing parts, by means of which the gap dimension can be adjusted when the two housing parts are screwed together. The thickness of the intermediate ring is dimensioned such that when the second housing part is screwed in shortly before the presumed target position is reached, the upper edge of the walls, the ring and the collar of the housing parts come into contact. The set position of a pilot valve can be found by compressing the intermediate ring with a compression force. With this solution, it appears disadvantageous that the deformable intermediate ring must be used between the two housing parts. This solution appears to be relatively complex since the intermediate ring must first be inserted and positioned. Furthermore, it is provided that after reaching the desired position, the two housing parts are welded at their interface. Intermediate rings also have the disadvantage that they age over the course of their service life and leakages can then occur. Furthermore, the intermediate ring increases not only the material costs, but also the assembly times, so that the manufacture of the injector becomes more expensive.

From DE 101 50786 AI a method and a device for the automatic setting of injectors is also known. In this device or method, the two housing parts of an injector, which has a piezoelectric actuator as the drive unit, are screwed together. The device detects the current angular position and the applied torque during the entire screwing process. A banjo bolt or nut, which is used with an open-ended wrench, serves as the setting torque Device is twisted. Furthermore, a voltage is applied to the actuator during the screwing process and the opening of the injector (diesel injector) is observed. The screwing process is switched off when the diesel injector opens. However, it is not apparent from this document which components absorb the change in length of the injector, in particular its shortening, when screwing. This problem occurs in particular when the two housing parts are to be screwed together with a nut, for example a nozzle clamping nut. The use of an elastic intermediate ring is not apparent from this document.

The object of the invention is to simplify the setting of a gap dimension or an idle stroke of the actuator unit in a fuel injector. This object is achieved with the features of the main claim.

In the fuel injector according to the invention it is provided that the two housing parts, which are formed by the injector housing and the nozzle housing, are screwed directly by means of a nozzle clamping nut. In order to set the required gap size, the two housing parts are pressed together by the nozzle clamping nut until the gap dimension is reached. This type of assembly has the advantage that no deformable intermediate ring is required between the two housing parts, since the housing material itself is so elastic that it can absorb the slight shortening that occurs when the housing parts are pressed together. It is also considered to be particularly advantageous that the screw connection can be loosened again and the adjustment process for the gap dimension can be repeated without additional measures being necessary. As a result, the adjustment work for the gap dimension can be carried out much more easily and successfully, so that the reject rate can be significantly reduced in the series production of the injector. Even after a long period of operation of the injector, a possible Required recalibration of the gap dimension is possible without any problems.

The measures listed in the dependent claims provide advantageous developments and improvements to the fuel injector specified in the main claim. It is considered to be particularly advantageous that in particular a very small gap dimension can be set, which for a piezoelectric actuator unit is in the range from 10 to 30 μm and is, for example, 20 μm and can be set with great precision but without great effort.

In order to further simplify the assembly process for the fuel injector and to achieve a defined assembly position for the actuator unit, provision is made for a base plate to be arranged on the lower end face of the actuator unit. This base plate is designed so that it lies exactly in the same plane with the lower cross-sectional area of the injector housing.

A particularly simple method for arranging the cross-sectional area and the cross-sectional plane in the same plane can be achieved by simple surface grinding. Component tolerances, which naturally always occur in production, do not have to be taken into account. They are compensated for automatically.

In order to prevent the lower cross-sectional plane of the injector housing from deforming when the two housing parts are pressed together, it is provided that the housing material is hardened at the corresponding points.

Furthermore, it is envisaged alternatively to harden the upper cross-sectional plane of the nozzle housing in order to obtain a good and tight-fitting press fit. A very simple method for setting the desired gap dimension also consists in extending the actuator unit exactly by the value that corresponds to the desired gap dimension by applying a corresponding voltage. In order to check the gap dimension during the pressing together of the two housing parts, it then only needs to be monitored at which angle of rotation of the nozzle clamping nut or at what point in time the valve is opened. A measurement of the torque or other parameters is not necessary. This allows the adjustment process for the gap dimension to be automated, for example, in a very simple manner.

The solution of using compressed air to monitor the opening of the valve also appears to be particularly advantageous. For this purpose, a compressed air hose is connected to the fuel injector and the escape of air at the valve is observed when it is opened when the gap is reached.

If the gap dimension is set automatically, the screwing process is stopped as soon as the valve opens and the compressed air escapes.

An embodiment of the invention is shown in the drawing and is explained in more detail in the following description.

FIG. 1 shows a fuel injector in a schematic representation,

FIG. 2 shows a detail of a longitudinal section through a fuel injector,

Figure 3 shows an enlarged longitudinal section, the arrangement of the idle stroke with the gap dimension and

FIG. 4 shows a flow diagram for the assembly and adjustment of the gap dimension. FIG. 1 shows a schematic illustration of a fuel injector 10 of the type used, for example, for injecting gasoline or diesel oil in a common rail injection system. The fuel injector 10 has an upper housing part 11 and a lower housing part 16, the two housing parts 11, 16 being axially assembled and held together by means of a nozzle clamping nut 17 which is pushed over the lower housing part 16 from below. The nozzle clamping nut 17 preferably has a threaded part (internal thread) on its upper region, which is joined to a corresponding threaded part of the upper housing part 11 (external thread). Position A shows a corresponding thread groove.

The upper housing part 11 is designed as an injector housing and has an actuator unit in its interior, as will be explained in more detail later in relation to FIG. 2. The lower housing part 16 is designed as a nozzle housing and has in its interior a nozzle unit with a valve through which the spray holes located at the lower tip of the nozzle housing 16 can be opened when the actuator unit 12 is actuated. After the nozzle clamping nut 17 has been tightened, a gap A is formed between the nozzle clamping nut 17 and the injector housing 11. For the sake of completeness, it should be mentioned that the fuel injector 10 can be fastened to an engine block by means of a clamping claw 5. The clamping claw 5 engages in a groove in the upper region of the injector housing 11. Furthermore, a fuel connection 24 and an electrical connection 23 are provided in the head region of the injector housing 11.

The sectional view of FIG. 2 essentially shows the arrangement of the actuator unit 12 inside the injector housing 11. The actuator unit 12 is constructed from a piezoelectric ceramic material which is encased by a tubular spring 12a. The head part of the actuator unit 12 is with the injector housing 11 constricted at this point. Furthermore, an electrical connection 23 is provided, via which the actuator unit 12 can be controlled.

At the lower end of the actuator unit 12 there is a base plate 13 which can be moved in the axial direction when an electrical voltage is applied.

The actuator unit 12 is installed in the injector housing 11 such that when the actuator unit 12 is at rest, the lower one

Cross-sectional area 20 of the base plate 13 lies in the plane of the lower cross-sectional plane 21 of the injector housing 11. For exact positioning, provision is made to adapt the cross-sectional area 20 and the cross-sectional plane 21 by surface grinding.

In an alternative embodiment of the invention, the base plate 13 can also be manufactured with an undersize or installed so that its lower cross-sectional area 20 lies above the cross-sectional plane 21 of the injector housing 11.

A valve plate 14 is arranged below the base plates 13 and is connected to a nozzle unit 15 (not shown in more detail in FIG. 2). The preferred solution is to manufacture the valve plate 14 with an undersize, so that the gap dimension s can be set when the two housing parts 11, 16 are pressed together.

In the subject matter of the invention, the installation dimension can thus be selected such that the base plate 13 and / or the valve plate 14 are adapted accordingly to the gap dimension s to be set. When the actuator unit 12 is activated, this gap dimension s must first be overcome before the nozzle unit 15 can be actuated. Since the linear expansion of the actuator unit 12 is very small and, depending on the piezoceramic used and the overall length of the actuator unit, is, for example, only in the range up to approximately 50 μm, the idle stroke should be set as low as possible for optimal use of the actuator stroke. On the other hand, it should be noted that even under worst-case conditions, in particular at high ambient temperatures, such as occur in the engine area, a reliable closing and opening of the spray holes of the nozzle unit 15 is guaranteed. It has proven to be advantageous if the gap dimension s is preferably selected in the range between 10 to 30 μm, for example 20 μm.

FIG. 3 shows an enlarged detail of the area of the fuel injector 10 in which the idle stroke with the gap dimension s is arranged. The injector housing 11 with the actuator unit 12 can be seen in the upper area of FIG. Furthermore, an opening is provided through which the electrical connection 23 for the actuator unit 12 is guided, so that the actuator can be controlled with the voltage (actuator voltage) U.

At the lower end of the actuator unit 12, the base plate 13 is arranged, which is firmly connected to the actuator unit 12 and is movable in the axial direction. Below the base plate 13, with the spacing of the gap dimension s, is the valve plate 14, which is connected to the nozzle unit 15. The gap dimension s, of course, only arises when the actuator unit 12 is not activated. A thread groove A can be seen at the transition between the injector housing 11 and the nozzle clamping nut 17. In this area there is also a thread by means of which the injector housing 11 is non-positively connected to the nozzle housing 16 by means of the nozzle clamping nut 17.

FIG. 4 shows a flowchart which relates to the assembly of the individual parts of the fuel injector 10 and indicates how the idle stroke is set with the gap dimension s. The setting is preferably carried out with a corresponding automatically controlled device, as described for example in DE 10150786 AI. First, the injector housing 11 is clamped into the device in position 31. A rod filter is installed in position 32. The rod filter is used to filter out small suspended particles that may be in the fuel. A cylinder pin is pressed in at position 33. The actuator unit 12 with the base plate 13 is then inserted in position 34. In position 35, the parts are aligned with respect to the lower cross-sectional area 20 of the injector housing 11, optionally ground flat, and the valve plate 14 is mounted. In position 36, the nozzle housing 16 is mounted with the nozzle unit 15. In a preferred embodiment of the invention, the valve plate 14 is made with an undersize so that when assembled before the nozzle clamping nut 17 is tightened, the distance from the base plate 13 is somewhat larger than the gap dimension s. Then the nozzle clamping nut 17 is mounted in position 37. In position 38, the idle stroke is adjusted with the gap dimension s, as previously described. A check is made in position 39 as to whether the gap dimension s has reached the desired value. If this is not the case, the fuel injector 10 arrives in position 40 for reworking with renewed adjustment. In the other case, when the gap dimension s has reached the setpoint, the screwing process is ended in position 41.

Claims

claims

1. Fuel injector (10) with an injector housing (11), with a nozzle housing (16) and with a nozzle clamping nut (17), the two housing parts (11, 16) being arranged axially on the end face and by means of the nozzle clamping nut (17) with one Detachable screw connection (18) are joined so that an actuator unit (12) is arranged within the injector housing (11) in such a way that its upper end face is firmly connected to the injector housing (11) and its lower end face when a voltage (U) is applied. extends downward that a nozzle unit (15) is arranged in the nozzle housing (16) and can be actuated by the actuator unit (12), and that between the actuator unit (12) and the nozzle unit (15) there is an idle stroke with a defined gap dimension (s) is adjustable, characterized in that the injector housing (11) and / or the nozzle housing (16) is made of a compressible steel material, that the nozzle unit (15) or its nozzle plate (14) and / or the actuator unit (12) or its base plate (13) are made with an undersize in relation to an installation position and that the nozzle clamping nut (17) can be tightened until the injector housing (11 ) and / or the nozzle housing (16) the predetermined gap dimension (s) is reached.

2. Fuel injector according to claim 1, characterized in that in the case of a piezoelectric actuator unit (12) the gap dimension (s) is in the range 10 to 30 μm, for example 20 μm.

3. Fuel injector according to claim 1 or 2, characterized in that the nozzle clamping nut (17) is detachable and the adjustment process for the gap dimension (s) can be repeated.

4. Fuel injector according to one of the preceding claims, characterized in that the actuator unit (12) is firmly connected at its lower end face to a base plate (13) and that in the rest position of the actuator unit (12) the lower cross-sectional area (20) of the base plate (13) coincides with a lower cross-sectional plane (21) of the injector housing (11).

5. Fuel injector according to claim 4, characterized in that the accuracy of fit for the cross-sectional area (20) and the cross-sectional plane (21) can be produced by surface grinding.

6. Fuel injector according to one of the preceding claims, characterized in that the lower cross-sectional plane (21) of the injector housing (11) is surface-hardened.

7. Fuel injector according to one of the preceding claims, characterized in that the upper cross-sectional plane of the nozzle housing (16) is hardened.

8. Fuel injector according to one of the preceding claims, characterized in that to adjust the gap dimension (s), the actuator unit (12) by means of a voltage (U) can be extended by the value of the gap dimension (s).

9. A fuel injector according to claim 8, characterized in that compressed air can be connected to a fuel connection (24) of the fuel injector (10) for test purposes.

10. Fuel injector according to one of claims 8 or 9, characterized in that the screwing process of the nozzle clamping nut (17) is stopped when the nozzle begins to open.