EP0279904B1 - Tube-shaped ceramic body - Google Patents

Abstract

A tubular ceramic body for gas passages in a cylinder head of an internal combustion engine comprises a tubular piece having an opening, two separate tubular portions each having an end side and provided with an opening at the end side, the tubular portions merging into the tubular piece in a transition region, and a connection provided between the tubular portions at least in the transition region of the tubular portions into the tubular piece, the ceramic body being formed as a one-piece member produced in a single sintering process from a single material, and the connection of the tubular portions being formed by a common wall.

Description

The invention relates to a tubular ceramic body according to the preamble of claim 1. Such a component in the form of a pants-shaped tube is known from DE-C 33 46 394. There, a connection is provided to support the two pipe sections, which is intended to provide sufficient resistance to the pressures that occur when the ceramic body is poured into the cylinder head. The connection should consist of zirconium oxide applied by means of plasma spraying, while the ceramic tube itself should consist of tialite (aluminum titanate).

A disadvantage of this known ceramic tube is the formation of ceramic tube and connection from different materials with very different thermal coefficients of linear expansion and modulus of elasticity. This creates temperature-related stresses - especially when pouring - but also during operation different thermally induced stresses in the elements made of different materials known ceramic body. There is therefore a risk of crack formation in the entire ceramic body, but in particular on the contact surfaces of the two materials. Stress peaks in the ceramic but also in the cast material are to be expected as further disadvantages, which can occur when the melt cools down in connection with the strongly different deformation behavior of the different materials (modulus of elasticity). But even the use of a uniform material would only lead to limited success in the case of a subsequent attachment of the connection to the already finished sintered tube body, which would require a second heating step, because then the occurrence would occur as a result of different shrinkage of the already finished sintered tube or the connection that is still to be sintered of cracks must be expected. Another disadvantage is that there is only a low bond strength between the connection and the actual tubular body. In the case of a connection made by plasma spraying, a different microstructure also arises - even when using the same raw material class - between the ceramic body which can usually be produced by slip casting and subsequent sintering and the connection formed by plasma spraying. This creates the disadvantages described above. It has also been shown that, in particular, the inner sides of the pipe sections, that is to say the points at which support is to be provided by means of the connection, are particularly at risk when the ceramic body is poured in.

The object of the invention is to provide a tubular ceramic body with two separately running pipe sections which merge into a single piece of pipe, which opposes an increased resistance to the pressure forces of the molten metal occurring when the ceramic pipe is poured in, in particular between the pipe sections.

This object is achieved in an object according to the preamble of claim 1 by its characterizing features.

The "one-piece" design of the ceramic body according to the invention, i. H. Both the actual pipe body and the connection between the two pipe sections, as a result of the molding from a slip casting compound and the production in a single sintering process, lead to the formation of a uniform and homogeneous structure from a uniform raw material composition and to the ceramic body having an approximately equal density and everywhere Has porosity.

The advantages of the invention consist, inter alia, in that, as a result of the one-piece design of the ceramic body, a tubular body is formed from a uniform material and requires only a single sintering process. The disadvantages known from the prior art of a low bond strength between the individual pipe sections and the connection between them are also avoided in this way like the previously existing disadvantage of insufficient component strength of a ceramic tube with tube sections that have constant wall thicknesses everywhere.

The decisive advantage is, however, that the ceramic body has the same range of properties everywhere due to its one-piece design, i.e. has, for example, almost the same thermal expansion coefficient and almost the same modulus of elasticity at all points and, as a result, no different stress states - neither in the ceramic body itself nor in the metal casting that envelops the ceramic body.

A particularly advantageous embodiment relates to the formation of the ceramic tube from aluminum titanate. Although this material has a considerably lower strength than other ceramic materials, such as zirconium oxide, it has already been proposed for the formation of tubular ceramic bodies in exhaust gas lines because it has a low coefficient of linear expansion and has excellent thermal insulation properties. In the past, however, difficulties repeatedly occurred because damage to the ceramic tube occurred, in particular when casting with metals, and here in particular when casting with ferrous metals.

If in detail the shape and dimensions of the ceramic tube can also be significantly determined by the design of the cylinder head, however, according to a preferred embodiment of the invention, a wall thickness of the common wall has proven to be suitable, which is 0.8 to 6 cm, preferably 1 to 2 cm, measured on an imaginary one Line between the two centers of the inlet openings of the pipe sections.

As a result of the one-piece design, the structure of the common wall lying between the two pipe sections can be used in an outstanding manner as a supporting function when lateral pressure forces act on the outer walls of the pipe sections. According to a particularly preferred embodiment of the invention, there is a ratio of 1: 2.5 to 1: 5 between the thickness of the outer walls and the thickness of the common wall - between the two pipe sections.

The valve-side end face lying in the region of the inlet openings of the two pipe sections is preferably oval, because this avoids the occurrence of stress peaks in the metal and in the ceramic as a result of the homogeneous transitions from thick to thin places. There are also no material accumulations in the casting, so that no locally different cooling zones occur during cooling.

If the construction of the cylinder head requires it, according to a further embodiment of the invention, the valve-side can be designed End surface with a cross section in the form of an eight. It is preferred if the web thickness - measured perpendicular to an imaginary line that runs through the center points of the inlet openings of the two pipe sections - corresponds at its narrowest point to approximately half the inside diameter of the inlet openings of the two pipe sections.

In any case, the outer contours of the individual sections of the ceramic tube should merge harmoniously.

Bores for the use of valve guides can already be provided in the manufacture of the ceramic body according to the invention, but alternatively, such bores can also be made subsequently on the already cast-in ceramic body.

According to the invention, the tubular ceramic body can be designed as a so-called downpipe, so that the common wall of the two pipe sections has a wall thickness that decreases in the direction of the transition area of the pipe sections into the pipe section. However, an embodiment is also possible in which the pipe sections run largely parallel and the common wall has an almost constant wall thickness. The last form described is used when the exhaust valves are arranged side by side in a cylinder. The former form is used when the exhaust valves are in series are arranged, each seen in the direction of the engine block.

Figur 1

einen hosenförmig ausgebildeten Keramikkörper von der Seite gesehen;

Figur 2

eine Frontansicht in Richtung des Pfeiles II auf Figur 1

Figur 3

eine Draufsicht in Richtung des Pfeiles III auf Figur 1;

Figur 4

einen Schnitt längs der Linie IV-IV in Figur 2, zum einen zeigend eine Eingangsöffnung samt dazugehöriger Bohrung für eine Ventilführung sowie die Austrittsöffnung;

Figur 5

einen Längsschnitt durch die Gesamtheit der Rohrstücke, in welche die Abgasströme eintreten, samt dem die Austrittsöffnung aufweisenden Rohrstück entsprechend der Linie V-V in Figur 4, also zeigend das gesamte Keramikrohr, aufgeschnitten;

Figur 6

eine Unteransicht in Richtung VI unter Figur 1 bzw. unter Figur 4;

Figur 7

einen ebenen Vertikalschnitt gemäß Ebene VII-VII der Figur 8, zeigend zwei Einschnitte je einen ober- und unterhalb der gemeinsamen Wandung zwischen beiden Rohrstücken einer weiteren Ausführungsform;

Figur 8

eine perspektivische Darstellung dieser weiteren Ausführungsform des Keramikrohres nach Fig. 7 schräg von unten und einer Seite gesehen;

Figur 9

einen Keramikkörper mit parallel verlaufenden Rohrabschnitten im Längsschnitt;

Figur 10

eine Untersicht in Richtung des Pfeiles X unter Fig. 9.

Show it:

Figure 1

seen a trouser-shaped ceramic body from the side;

Figure 2

a front view in the direction of arrow II on Figure 1

Figure 3

a plan view in the direction of arrow III on Figure 1;

Figure 4

3 shows a section along the line IV-IV in FIG. 2, showing an inlet opening together with the associated bore for a valve guide and the outlet opening;

Figure 5

a longitudinal section through the entirety of the pipe sections into which the exhaust gas flows enter, including the pipe section having the outlet opening according to the line VV in FIG. 4, ie showing the entire ceramic pipe, cut open;

Figure 6

a bottom view in the direction VI under Figure 1 or under Figure 4;

Figure 7

a flat vertical section according to level VII-VII of Figure 8, showing two incisions, one above and below the common wall between the two pipe sections of a further embodiment;

Figure 8

a perspective view of this further embodiment of the ceramic tube according to Figure 7 seen obliquely from below and one side.

Figure 9

a ceramic body with parallel Pipe sections in longitudinal section;

Figure 10

a bottom view in the direction of arrow X in FIG. 9.

The ceramic tube (1) shown in FIGS. 1 to 6 consists of the two tube sections (2, 3) and the tube section (4). The pipe sections (2, 3) form the shape of a pair of pants and unite in the transition area (9) to form the pipe section (4). In line with the two pipe sections (2, 3), holes (7, 8) are provided for the use of valve guides.

The pipe sections (2, 3) are curved at an angle β determined by the shape of the cylinder head (FIG. 4).

The pipe sections (2, 3) have equally thick outer walls (5) with the thickness S1. The pipe section (4) is also of the same wall thickness S1. A common wall (6) is arranged between the two pipe sections (2, 3) and has a maximum wall thickness S2 in the area of the inlet openings (10, 10a) of the pipe sections (2, 3). The pressure forces that occur due to the casting are indicated by the arrow P in FIG.

The area comprising the inlet openings (10, 10a) forms the valve-side end face F and is designed in an oval shape in cross section (FIG. 6).

In the ceramic body shown in FIGS. 7 and 8, which otherwise corresponds to the exemplary embodiment shown in FIGS. 1 to 6, incisions E1, E2 are made between the inlet openings (10, 10a) of the pipe sections (2, 3) so that the outer walls (5) the pipe sections (2, 3) are cut into an eight and the valve-side end face F 'has the shape of an eight.

The transition of the outer walls (5) of the pipe sections (2; 3) into the common wall (6) takes place at their outer contours at the turning point designated by W (turning point of the contour profiles).

The web thickness S3 corresponds to approximately half the value of the inside diameter of the inlet openings (10, 10a).

The tubular ceramic body (1 ') shown in FIGS. 9 and 10 has parallel pipe sections (2', 3 ') which open into the pipe section (4') in the transition region (9 '). The pipe sections (2 ', 3') are connected by a common wall (6 ') with the wall thickness S2', the wall (6 ') from the area of the inlet openings (10', 10a ') to the transition area (9') is formed with a constant wall thickness. The outer walls (5 ') of the pipe sections (2', 3 ') and the pipe section (4') have a constant wall thickness S1 '. The valve-side end face F '' is kidney-shaped in this embodiment.

Claims (7)

1. Tubular ceramic body (1, 1') for gas-conducting channels in the cylinder head of an internal combustion engine having:

   a) two separate tube sections (2, 2'; 3, 3'), having openings at their ends, which pass into a single piece of tube (4, 4') having an opening,

   b) a connection constructed between the two tube sections at least in the transition region (9, 9') of the two tube sections (2, 2'; 3, 3') into the piece of tube (4, 4'),

   characterised in that

   1. the ceramic body (1, 1') including the connection between the two tube sections (2, 2', 3, 3') is constructed in one piece and is manufactured by moulding in a single sintering process and has a uniform and homogeneous structure consisting of a uniform raw material composition,

   2. the connection of the tube sections (2, 2', 3, 3') is formed by a common wall (6, 6').
2. Tubular ceramic body according to claim 1, characterised in that the material of the ceramic body (1, 1') is aluminium titanate.
3. Tubular ceramic body according to claim 1 or 2, characterised in that the ceramic body (1, 1') has in the region of the inlet openings (10, 10', 10a, 10a') of the tube sections (2, 2', 3, 3') a planar valve-side end surface F, F', F'' (Figures 2, 6, 8, 9, 10).
4. Tubular ceramic body according to any one of claims 1 to 3, characterised in that the valve-side end surface F, F' is constructed to have an oval cross-section (Fig. 6).
5. Tubular ceramic body according to any one of claims 1 to 3, characterised in that the valve-side end surface F, F' has a cross-section in the form of a figure eight.
6. Tubular ceramic body according to any one of claims 1 to 3 and 4 or 5, characterised in that the common wall (6) decreases in thickness in the direction towards the transition region (9) (Figure 5).
7. Tubular ceramic body according to any one of claims 1 to 3 and 4 or 5, characterised in that the common wall (6') has a constant thickness in the direction towards the transition region (9').

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