DE102005047275B4 - Pressure tube with deformed connection head - Google Patents

Abstract

Pressure pipe with a connection head (1) produced by cold forming truncated cone at one end of a pipe (16) for connection to an injection system of an internal combustion engine, wherein the connection head (1) on a lateral surface opposite a circumferential sealing surface (13) for sealing the connection head (1) a connection piece, on a cover surface (18) has a tube opening (19) and on a side opposite the top surface a pressure shoulder (10) which abuts the pipe (16), for introducing a required for the sealing of the sealing surface (13) biasing force , wherein an outer surface of the pipe (16) with an area of the pressure shoulder (10) encloses an angle between 100 ° and 110 °, the inner surface (17) of the pressure tube in the region of the connection head (1) forms an inner cone (9), such in that the inner diameter of the pipe is at the base of the inner cone (9), ie the expansion on the end face of the pressure tube, in a range of 1.02 to 1.4 x pipe inside diameter of the pipe, and the lateral surface of the connection head (1) in the region between the sealing surface (13) and pressure shoulder (10) has a substantially concave bulge (12).

Description

The present invention relates to a pressure tube with a reshaped connection head.

Pressure pipes, as they are based on the invention, are used as fuel injection pipes for supplying the fuel to the injection system or as hydraulic pipes. In order to connect the pressure pipes sealingly to another component, the ends of the pressure pipes are formed in the shape of a truncated cone. As a cost-effective variant for the production of such connection heads, the cold forming has proven in the prior art. A product of the method known from the prior art is disclosed, for example, in the published patent application US 6,286,556 B1 and DE 103 58 373 A1 represented by fuel pipes.

This prior art is also enclosed 1 shown, a cross section showing the frustoconical connection head and the tube interior deformed by compression of the pressure tube. The seal against a component to which the pressure tube is to be connected, takes place in this embodiment of the prior art on the oblique lateral surfaces of the connection head and a union nut (not shown), via the pressure shoulder 2 exerts a biasing force on the pressure tube, so that the pressure tube or the oblique lateral surface of the connection head is pressed against a corresponding seat of the component to be connected.

In the prior art, however, arises due to the displacement of the tube shell during cold forming or upsetting in the radial direction to the outside, on the inner diameter of the tube an annular, sharp crease 4 , However, during operation, the fuel injection tube is exposed to high, swelling internal pressures, causing the compression fold 4 can lead to a fatigue breakage of the pressure tube. Furthermore, the inner diameter in the region of the connection head is not uniform, but has various constrictions 5 on, which lead to the throttling of the fuel flow, and also due to the cross-sectional changes mean pressure changes and thus cavitation. In the prior art, this uneven inner diameter and the compression fold 4 encountered in that the inner diameter of the tube is wiped on the front side by means of a conical reamer up both crushed fold 4 as well as constrictions 5 are eliminated. In this post-processing, which has an adverse effect on the surface finish inside the pipe, it must be ensured that the upset fold created by the cold forming 4 is completely removed.

In the field of high pressure technology, e.g. at injection pressures of about 1600 bar and above, as they are used in marine engines, the problem presented above comes in a special way in the foreground. One way to counteract high pressures is to adjust the diameter ratio between the outer and inner diameters of the tube accordingly, i. to choose a larger compared to the inner diameter outer diameter and thus to form a thick tube shell. However, even this measure has its limitations, so that the use of pipes made of higher-strength material is required. However, it decreases with increasing tensile strength, the ductility of the material and so the formability. For pipe materials with an elongation at break of A <20%, there is the danger of a significantly deeper formation of the compression fold during the shaping of the connection head. By rubbing using the above-mentioned conical reamer this crease is then often no longer completely eliminate.

The already mentioned publication DE 103 58 373 A1 proposes to avoid these folds folds to use a stepped connection plate on the pressure shoulder of the connection head. A disadvantage of this prior art is the use of the elaborate step-shaped connection disk and the fact that the deformation of the inner diameter during cold forming can not be prevented by the method selected in this prior art. From the prior art it is therefore known that a reshaping of the pressure pipes in high-strength steels is completely dispensed with, and instead the connection head of the pressure pipe is formed by means of machining forms.

Furthermore, from the DD 225 480 A1 a pressure pipe with a truncated cone-shaped connection head at one end of a pipeline for connection to an injection system, wherein the connection head has a peripheral sealing surface on a lateral surface, a pipe opening on a top surface and a pressure shoulder on a side opposite the top surface, for introducing a required for the sealing of the sealing surface biasing force. An outer surface of the pipeline encloses an angle of greater than 90 ° with an area of the pressure shoulder. Also the DE 40 32 554 A1 , the JP 2005-2806 A and the DE 39 27 288 A1 , as well as the DE 100 61 015 A1 each show a device with all these features.

From the illustrated prior art, it is an object of the present invention to provide a new pressure tube, which after cold forming a connection head neither a Buckle fold, still a constricted inner diameter.

This object is achieved according to claim 1 of the invention. The dependent claims are advantageous embodiments of the invention.

The invention comprises a pressure tube, e.g. can be used as a fuel injection pipe of an injection system of a diesel engine, with a truncated cone-shaped connection head. The pressure tube therefore has a pipeline and a connection head. The connection head is made at the end of a pipeline by cold forming. The connection head, which essentially forms a truncated cone, consists of a lateral surface on the side, a cover surface at the end of the tube and a part of a base surface of a geometric truncated cone. The interior of this geometric base is integrally connected to the rest of the pressure tube, and the exposed, outer part of the base surface is not on the same plane as the inner part of the base, so the connection head is referred to here as a truncated cone and does not form a geometrically perfect truncated cone. On the lateral surface, the surface for sealing the connection head with respect to a counterpart is formed, the counterpart being e.g. may be part of an injection system for diesel engines. At the top surface of the pipe opening is formed and on the cover surface opposite side is formed a pressure shoulder for introducing a required for the sealing of the sealing surface biasing force. The outer surface of the unformed pressure tube, i. the pipeline, encloses an angle of> 90 ° with a surface of the pressure shoulder.

Due to this arrangement of pressure shoulder and outer surface of the pressure tube, the pressure shoulder is at least slightly beveled, whereby a more homogeneous fiber profile is achieved in the connection head. Due to the more homogeneous fiber flow, the operational stability of the connection head, in particular at the critical region of the transition from the pressure shoulder to the outer surface of the pressure pipe, is improved. Furthermore, the compression fold is reduced by this embodiment of the pressure shoulder.

According to the invention, the inner surface of the pressure tube in the region of the connection head tapers conically from the outside to the inside. This taper is introduced in the upsetting process by means of a corresponding Gesenkdornes. That is, during the upsetting, there is a slight widening of the inner diameter of the pressure tube. By using the mandrel on the die in the production of the pressure tube, therefore, there is no deformation of the inner surface of the pressure tube, so that a reworking by means of a conical reamer to form a uniform inner diameter is no longer necessary. The surface quality on the inside of the pressure tube is thus improved in the region of the connection head.

According to the invention, the lateral surface of the connection head in the region between the sealing surface and the pressure shoulder on a substantially concave bulge. The bulge at the connection head, which is created by a correspondingly shaped die during cold forming, leads to a reduction of the material volume below the pressure shoulder. It is therefore ensured during the cold forming that the material of the pressure tube is not pushed in the direction of the inner diameter, but away from it, so that it can not lead to constrictions on the inner diameter.

According to a further embodiment of the invention, a bevel is provided as an autofrettage sealing surface on the pipe opening of the connection head. This bevel serves to prevent damage to the sealing surface during autofrettage. Fuel pressure pipes are usually autofrettiert to fatigue increase. For this purpose, the tube is briefly exposed to a high internal pressure, which leads to the development of residual compressive stresses after pressure relief due to plastic deformation. Since the autofrettage pressure is significantly above the later operating pressure of the pressure tube, a seal on the actual sealing surface on the lateral surface of the frustoconical connection head should be avoided. Because the necessary to ensure tightness in the autofrettage high forces on a Autofrettagedichtfläche, lead in the pressureless state to a plastic deformation and thus damage to the Autofrettagedichtfläche. The chamfer can be formed by a corresponding design of the die already during compression of the connection head. Accordingly, no further processing of the pressure pipe connection head is necessary as a result of the embodiments according to the invention mentioned here when the connection head is produced with the production process described by means of the die according to the invention mentioned below.

According to a further embodiment of the invention, the sealing surface is formed on the lateral surface spherical. As a result, the pressure distribution at the sealing surface, in particular at an angular deviation of the axis of the connection head with respect to the axis of the counterpart, is improved. Furthermore, it is possible to regrind this easier with mechanical damage to the sealing surface. Because in conjunction with the concave bulge of the connection head ensures that when regrinding the sealing surface no grinding notches are formed on the lateral surface of the connection head.

According to a further embodiment of the invention, the pressure shoulder is substantially planar, whereby the assembly with and the geometry of a pressure ring, which rests when the pressure tube is installed on the pressure shoulder, is simplified.

Furthermore, a die for upsetting a pressure tube to a connection head with a substantially frusto-conical, inwardly tapering recess, which corresponds to an outer contour of the connection head to be compressed, is provided. In this case, the die has a shape that generates a connection head during compression, which has a pressure shoulder, which forms an angle of> 90 ° with the outer surface of the pipe of the pressure tube.

The die need not necessarily be formed in one piece here, but preferably consists of two parts, wherein a first part is a counterpart of a second part. That a first part is pressed against the pipe end, wherein the second part forms the pressure shoulder of the connection head.

The recess has a convex bulge in the first part of the die, so that the connection head is formed with the above-mentioned bulge on the lateral surface.

A mandrel is provided in the first part of the die, which is inserted into the tube opening of the pressure tube, so that it can not lead to deformation of the inner diameter of the pressure tube to be compressed. For this purpose, the outer diameter of the mandrel must substantially correspond to the inner diameter of the pressure tube.

The mandrel may also be tapered. In this case, a base surface of this mandrel has an outer diameter which is greater than the inner diameter of the pressure tube to be compressed. Therefore, when upsetting, the inner diameter of the pressure tube widens, which further prevents deformation of the inner diameter.

In addition, the die may be designed such that a further bevel is provided on the base surface of the mandrel in order to give the pressure tube at the tube opening a chamfer. As already mentioned, a chamfer at the pipe end is advantageous in that it can be used as a seal of the pressure pipe in the autofrettage process. As a sealing surface according to the invention therefore not the later sealing surface of the pressure tube is used. In order to enable the most cost-effective production of the chamfer, it is formed with the cold forming process, which is why the corresponding slope is provided on the die.

The mandrel of the die may also be frusto-conical and a further chamfer may be provided on the top surface of the mandrel to more easily align the mandrel coaxially with the pressure tube.

• 1: ein Druckrohrende mit Anschlusskopf im Querschnitt, gemäß dem Stand der Technik;
• 2: ein Druckrohrende mit Anschlusskopf im Querschnitt, gemäß der vorliegenden Erfindung;
• 3: ein Gesenkteil im Querschnitt, gemäß der vorliegenden Erfindung.

The embodiments of the invention will be explained with reference to the accompanying drawings. It shows:

• 1 a pressure tube end with a connection head in cross-section, according to the prior art;
• 2 a pressure tube end with a connection head in cross-section, according to the present invention;
• 3 a swaging part in cross-section, according to the present invention.

2 shows the pipe end of a fuel injection pipe with a connection head ( 1 ) and a pipeline ( 16 ). The bevelled pressure shoulder ( 10 ) is based on a pressure ring ( 11 ), for example, when installing with a union nut (not shown) is needed. The lateral surface of the frustoconical connection head ( 1 ) has on the one hand a bulge ( twelve ) and on the other hand a sealing surface ( 13 ) on. The sealing surface ( 13 ) seals the pressure tube against a counterpart from the injection system (not shown). On the inner surface ( 17 ) of the pressure tube is in the region of the connection head ( 1 ) an inner cone ( 9 ) educated. The inner cone ( 9 ) forms the pipe opening ( 19 ) on the top surface ( 18 ). The pressure shoulder ( 10 ) forms with the outer surface of the pipeline ( 16 ) of the pressure tube at an angle greater than 90 °. Preferably, this angle is between 100 ° and 110 °. In this angular range the stress of the pressure ring ( 11 ) advantageous. The height H of the connection head ( 1 ) also has an influence on the buckling fold formation and should be in the range of 0.5 to 1.0 x outer diameter for pressure tubes with an outer diameter of> 10 mm. The inner pipe diameter at the base of the inner cone ( 9 ), ie the expansion on the front side of the pressure pipe, should be in a range of 1.02 to 1.4 x pipe inside diameter of the pipe. Because the connection head ( 1 ) on the sealing surface ( 13 ) is spherical, even with angular deviation between the axes of the pressure tube and the counterpart a uniform pressure distribution over the circumference of the sealing surface ( 13 ) can be achieved.

An embodiment of the second aspect of the invention, ie a first part of the die ( 7 ), which is pressed against the pressure tube end for upsetting, is in 3 shown in cross section. The die ( 7 ) has a thorn ( 8th ), which is frusto-conical. At the foot or at the base of the thorn is a slope ( 15 ) for the formation of the chamfer ( 14 ) on the connection head ( 1 ) intended. The top surface ( 6 ) is connected via a chamfer with the lateral surface of the truncated cone. The die part has a recess ( 20 ), the trough of the negative of the connection head to be compressed ( 1 ), which is why a bulge ( 3 ) is visible in the profile of the tub. The length of the mandrel should be at least 1.5 x the height H of the connection head ( 1 ) be.

LIST OF REFERENCE NUMBERS

1

connection head

2

Pressure shoulder in the prior art

3

bulge

4

edging fold

5

Constriction on the inside diameter

6

Top surface of the die

7

die

8th

mandrel

9

Inner cone

10

Pressure shoulder according to the invention

11

pressure ring

12

Bulge on the lateral surface

13

sealing surface

14

chamfer

15

slope

16

pipeline

17

palm

18

cover surface

19

tube opening

20

recess

Claims (4)

Pressure pipe with a connection head (1) produced by cold forming truncated cone at one end of a pipe (16) for connection to an injection system of an internal combustion engine, wherein the connection head (1) on a lateral surface opposite a circumferential sealing surface (13) for sealing the connection head (1) a connection piece, on a cover surface (18) has a tube opening (19) and on a side opposite the top surface a pressure shoulder (10) which abuts the pipe (16), for introducing a required for the sealing of the sealing surface (13) biasing force , wherein an outer surface of the pipe (16) with an area of the pressure shoulder (10) encloses an angle between 100 ° and 110 °, the inner surface (17) of the pressure tube in the region of the connection head (1) forms an inner cone (9), such in that the inner diameter of the pipe is at the base of the inner cone (9), ie the expansion on the end face of the pressure tube, in a range of 1.02 to 1.4 x pipe inside diameter of the pipe, and the lateral surface of the connection head (1) in the region between the sealing surface (13) and pressure shoulder (10) has a substantially concave bulge (12). Pressure tube after Claim 1 , characterized in that the tube opening (19) has at its periphery a chamfer (14). Pressure tube according to one of the preceding claims, characterized in that the sealing surface (13) is spherical. Pressure tube according to one of the preceding claims, characterized in that the pressure shoulder (10) is formed substantially flat.

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