WO2008031773A1

WO2008031773A1 - Expansion pipe

Info

Publication number: WO2008031773A1
Application number: PCT/EP2007/059403
Authority: WO
Inventors: Georg Bachmaier; Hellmut Freudenberg; Andreas GÖDECKE; Thomas Vontz
Original assignee: Siemens Aktiengesellschaft
Priority date: 2006-09-13
Filing date: 2007-09-07
Publication date: 2008-03-20
Also published as: DE102006042973A1

Abstract

The invention relates to an expansion pipe (1;9;10;15;19), comprising a wall (2) with a cross-sectional profile that has several wall segments (4) with a first basic form, each respective pair of wall segments (4) being connected by a shaped portion (5; 14; 16; 20) with a second basic form that differs from the first basic form.

Description

description

Dehnrohr

The invention relates to an expansion tube.

In particular, for leak-free gasoline and diesel high pressure injectors, piezoactuators are often operated in a high fuel pressure range. However, it must not be brought into contact with fuel components, for example to avoid corrosion. One possibility for arranging the piezoactuator is to introduce it hermetically sealed against fuel into an expansion tube or expansion tube. A free volume between Piezoaktuator and Dehnrohr is usually filled with a filling oil. The expansion tube also often serves as a biasing spring, which keeps the piezo actuator in the actuating direction to avoid crack propagation under tension.

One way of forming an expansion tube is to use a metal bellows. Previously proposed metal bellows with expansion tube function for isobaric media separation under high pressure can only be used for a limited temperature and pressure range. In the case of strong temperature or pressure fluctuations, the expansion or compression of the enclosed materials, eg. As the piezoelectric actuator and the surrounding filling oil, the metal bellows exposed to high voltage loads. This greatly shortens the service life and makes the component susceptible to failure in continuous operation. These, depending on the boundary conditions of the use, mechanical stresses must be kept as low as possible (depending on the material about 1 GPa, better below 500 MPa). In addition, z. T. consuming production processes necessary to realize suitable membrane shapes can. It is therefore the object of the present invention to provide a way to improve the longevity of expansion tubes under severe temperature or pressure fluctuations.

This object is achieved by a stretching tube according to claim 1. Advantageous embodiments, in particular the dependent claims individually or in combination can be removed.

For this purpose, the expansion tube has a wall with a cross-sectional profile, which has a plurality of wall segments of a first basic shape, of which two wall segments are connected by a shaping of a second, different basic shape to the first basic shape.

Under a same basic form forms are understood that differ only in their dimensions, z. B. sinusoidal wall sections with different "amplitude".

With this configuration, the enclosed volume can be minimized in a simple way. Due to the lower internal volume changes in volume of the filling material, eg. B. the piezoelectric actuator and the filling oil due to pressure or temperature fluctuations minimized. In addition, the flexibility or rigidity of the expansion tube can be adjusted by the design of the formations.

It is, in particular for receiving bodies with rotationally symmetrical cross-sectional area advantageous if the first basic shape of the wall segments is rotationally symmetrical.

It may then be particularly advantageous if the basic shape of the wall segments round, z. B. oval, but in particular circular, is.

But it may also be advantageous if the basic shape of the wall segments is n-angular, with n ≥ 4, z. B. quadrangular, especially square, or octagonal. It is advantageous for improving the mobility of the expansion tube if at least one molding has in each case a connection part for connection to a wall segment, and in each case a leg part for connection to a connection part and a connection part for connection of the leg parts

Straight leg parts, in particular, advantageously allow high mobility.

It may, depending on the specific embodiment, be advantageous if the leg portions are aligned substantially parallel to each other, run towards each other from the connection parts or run apart from the connection parts.

It may, depending on the specific embodiment, be advantageous if the connecting part is formed substantially halbkreisför- mig, arcuately formed with an angle smaller than 180 ° or arcuately formed with an angle greater than 180 °.

A particularly advantageous, because simple and yet accurate shaping is achieved when the expansion tube is formed by hydrostatic drawing or hydroforming. This is an inexpensive production process which can also be used for large quantities and which is suitable for mass production.

It is particularly advantageous in angular first basic form when the expansion tube is formed by hydrostatic pulling from outside to inside. In this case, for example, a tubular blank having a diameter corresponding to a maximum outer diameter of the finished hydrostatically formed wall can be used. By externally applied liquid pressure, the formations are formed inwardly against a die. there In general, the material is compressed by a certain percentage.

It is advantageous, in particular in the case of a round first basic shape, if the expansion tube is formed from inside to outside by hydrostatic drawing or hydroforming. In this case, the shaping takes place in such a way that a, in particular tubular, blank whose diameter corresponds to the minimum inner diameter of the finished expansion tube is used as the starting workpiece. The fluid pressure is applied from the inside, the formations are thus formed outwardly against a negative mold. The material stretch is generally greater in this type of production than in the inside shape. It must be ensured in these production processes that the material stretch remains below a predetermined maximum value (typically about 30% for austenitic steels), otherwise the wall will be damaged during the forming process.

In the following, the invention is explained in more detail purely schematically with reference to selected, not intended to limit the invention exemplary embodiments. Like components are indicated by like reference numerals.

1 shows a side view of a Dehnrohrs;

FIGS. 2 to 6 show various exemplary cross-sectional profiles of a stretching tube.

7 shows a plot of a maximum Dehnrohrspannung against a material stretch for a production of different cross-sectional profiles.

1 shows a side view of a substantially cylindrical expansion tube 1, which in the longitudinal direction along its longitudinal axis L in a bellows region B and a Dehnrohrbereich D is divided into two parts. In this expansion tube 1 a Piezoaktua- tor and filling oil are hermetically welded (not shown). The actuation direction of the bellows region B corresponds to the longitudinal axis L. The actuation direction of the expansion tube region D corresponds to the axis AA. In the following, the configuration of the Dehnrohrbereichs D in cross section along the section axis AA is further described.

2 shows the cross-sectional profile of the expansion tube 1 of FIG 1 along the section line A-A. The expansion tube 1 has a metallic wall 2 made of austenitic steel, which has an interior space 3 for receiving z. B. a piezo actuator (not shown) defined. The wall 2 has a cross-sectional profile having six wall segments 4 of a circular first basic shape with inner radius RO around the center M of the expansion tube 1, as indicated by the dotted line. The center M of the expansion tube 1 also corresponds to the position of the longitudinal axis L in the cross-sectional area.

Here and below are provided for clarity, only the components of the Dehnrohrwand 2 in a single, indicated by the dotted lines angle sector of 60 ° with reference numerals. The design in the other angular sectors is identical.

Each two wall segments 4 of the circular first basic shape are connected by a formation 5 (six in total) of a second basic shape different from the first basic shape. The second basic form here corresponds to an outwardly directed, closed, approximately U-shaped extension. The expansion tube 1 shown or its expansion tube region thus has a number of formations 5 corresponding 6-fold rotational symmetry in the cross-sectional plane.

In detail, each formation 5 in each case has a connection part 6 for connection or at the transition with an associated wall segment 4. The connecting part 6 is followed in each case by a straight leg part 7, wherein the leg parts 7 are aligned parallel to each other. The two leg parts 7 are formed by a semicircular connecting part

8 interconnected.

This expansion tube 1 has been formed by hydrostatic pulling an integral cylindrical base work piece (not shown) from inside to outside.

FIG. 3 shows a further embodiment of a cross-sectional profile of an expansion tube 9 in a representation analogous to FIG. 2.

In contrast to the embodiment of FIG. 2, the wall 2 of the expansion tube 9 is now vierzählig rotationally symmetric, thus has four formations 5.

4 shows a further embodiment of a cross-sectional profile of an expansion tube 10 in a representation analogous to FIG. 3

In contrast to the embodiment of FIG. 3, each of the four formations 11 of the expansion tube 10 is now formed so that the leg portions 13 are no longer arranged in parallel, but run towards each other from the connection parts 12 to the outside. The connecting part 14 is formed corresponding arcuate with an angle smaller than 180 °. This embodiment is easier to manufacture than the embodiments of FIG 2 and or FIG. 3

5 shows a further embodiment of a cross-sectional profile of an expansion tube 15 in a representation analogous to FIG. 2

In contrast to the also 6-fold rotationally symmetrical embodiment of FIG 2, the leg portions 17 of the respective formation 16 are also arranged parallel to each other, but the connecting parts 18 of the respective formations 16 are arcuate with an angle greater than 180 °, namely almost circular, formed. In addition, the leg portions 17 are compared to the embodiment of FIG 1 closer together, so have a smaller distance from each other. The running as a circular ring connecting parts 18 thus have a diameter which is greater than the distance of the leg parts 17th

This embodiment minimizes the stresses in the critical outdoor areas, thus optimizing the life.

In addition, in particular the formations 16 with long, straight legs 17 allow a good mobility of the wall 2. The formations 16 move similar to the legs of a pair of tweezers (opening or closing movement). Due to the long lever only small forces are necessary for this. The movement of the attachment point of the formations 16 in the circumferential direction changed, in particular in this embodiment, the wall circumference and thus the enclosed volume. Thus, the expansion tube can compensate for a large volume difference with small internal forces, which occurs, for example, as a result of a temperature-related volume increase or decrease or a pressure-related compression of the filling material. The improved mobility in turn leads to an extension of the life.

Alternatively, the leg parts need 17 z. B. also not be arranged in parallel, but z. B. in particular similar to FIG 4 converge.

FIG. 6 shows a further embodiment of a cross-sectional profile of an expansion tube 19.

In the now 5-fold rotationally symmetrical embodiment, the straight leg parts 21 of the formations 20 run apart from each other from the connecting pieces (without reference numerals) and are each separated by an arcuate connecting part 22 with an arc angle smaller than 180 ° over a transition radius (without reference numeral). connected. The Connecting parts 22 are shaped so that they lie on a common circle with outer radius Rl, as indicated by the dashed line, and that the connecting part 22 with length 1 at the outer radius Rl is so long that the critical material load is exceeded by bending. The

Basic shape of the formations 20 may, for. B. be referred to as a substantially funnel-shaped. The legs of the adjacent formations 20 should advantageously be seen from the outside parallel or slightly conically inclined, so that a molding of the expansion tube is particularly well possible.

In the embodiments shown, the additional volume can be kept small. Due to the low internal volume volume changes of the filling material are minimized by pressure or temperature fluctuations. This reduces the load on the wall and prolongs its life. In addition, a movement of the starting point of the formations in the circumferential direction changes the wall circumference and thus the enclosed volume. The expansion tube can thus compensate for low internal forces a large volume difference, which occurs for example by a temperature-induced volume increase or decrease or pressure-induced compression of the filling material. The improved mobility in turn leads to an extension of the lifetime.

7 shows a plot of a maximum Dehnrohrspannung in GPa against an approximated Materialverstreckung in% when producing a Dehnrohrs by means of hydrostatic pulling inwards for different cross-sectional profiles analogous to the embodiments of FIG 2 and FIG 3 with a different number of formations. As boundary conditions, an external pressure of 2000 bar and a filling with silicone oil and piezo material was assumed.

The maximum stresses in the expansion tube area are a measure of the Dehnrohrbeweglichkeit: the more flexible the expansion tube is, the smaller tensions occur. As noted above, for hydrostatic drawing, austenitic steels should typically be stretched below about 30%. For a good mobility of the wall, however, requires long trained formations that require a lot of material and thus generally produce a high material distortion in the manufacturing process.

The calculations for the assumed model assumptions show that for walls with up to 6 formations, the material stretch remains below the exemplary critical limit of 30% (vertical dotted line). At the same time, sufficient deformability of the membrane is ensured from 4 formations, so that the maximum stresses remain below the exemplary yield strength of approx. 1 GPa (horizontal dotted line).

Of course, the above invention is not limited to the embodiment shown. So other symmetry orders can be selected, for. B. quadrangular, hexagonal, octagonal, etc., z. B. with straight wall segments. Also, the Dehnrohrkörper does not need or sometimes not designed to be symmetrical. Also, the formations need not be the same shape, but are preferably arranged symmetrically; For example, different groups of formations may alternate. Also in the circumferential direction a-symmetrical leg parts are conceivable.

Claims

claims

1 . Expansion tube (1; 9; 10; 15; 1 9), characterized in that it has a wall (2) with a cross-sectional profile which has a plurality of wall segments (4) of a first basic shape, of which two wall segments (4) by a formation (5; 14; 16; 20) of a second basic shape different from the first basic shape.

2. expansion tube (1; 9; 10; 15; 19) according to claim 1, characterized in that the first basic shape is rotationally symmetrical.

3. stretching tube (1; 9; 10; 15; 19) according to claim 2, characterized in that the basic shape of the wall segments (4) is round, in particular circular.

4. expansion tube (23) according to claim 1, characterized in that the basic shape of the wall segments is n-angular, with n ≥ 4, is.

5. stretching tube (1; 9; 10; 15; 19) according to one of the preceding claims, characterized in that at least one formation (5; 14; 16; 20) has:

- Each one connecting part (6, 12) for connection to a wall segment (4); and

- one leg part (7; 13; 17; 21) for connection to a connection part (6; 12); and

in each case a connecting part (8; 14; 18; 22) for connecting two leg parts (7; 13; 17; 21).

6. Stretching tube (1; 9; 10; 15; 19) according to claim 5, characterized in that the leg parts (7; 13; 17; 21) are straight.

7. stretching tube (1; 9; 15) according to any one of claims 5 or 6, characterized in that the leg portions (7; 17) are aligned parallel to each other.

8. stretching tube (10) according to any one of claims 5 or 6, characterized in that the leg portions (13) of the connecting parts (12) converge towards each other.

9. stretching tube (19) according to any one of claims 5 or 6, characterized in that the leg portions (21) of the connecting parts (6) from diverge.

10. expansion tube (1; 9) according to one of claims 5 to 9, characterized in that the connecting part (8) is substantially semicircular.

11. Expansion tube (10; 19) according to one of claims 5 to 9, characterized in that the connecting part (14; 22) is arc-shaped with an angle smaller than 180 °.

12. Dehnrohr (15) according to any one of claims 5 to 9, characterized in that the connecting part (18) is arcuate formed at an angle greater than 180 °.