EP1485582A1

EP1485582A1 - Lightweight valve

Info

Publication number: EP1485582A1
Application number: EP03743371A
Authority: EP
Inventors: Arndt Bosler; Rainer Joos; Detlef Nowotni
Original assignee: DaimlerChrysler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2002-03-05
Filing date: 2003-03-04
Publication date: 2004-12-15
Also published as: DE10209770A1; WO2003074843A1; US20060005792A1

Abstract

The invention relates to a lightweight valve that consists of a valve base, the latter comprising a valve stem and a hollow valve cone, and a valve head cover, whereby the valve base is linked with the valve head cover by means of a material-displacing welding method. A weight-reducing cavity is defined between the valve cone and the valve head cover in the assembled state of the valve, said cavity being provided with a stability-enhancing support structure. Suitable welding methods are projection welding, capacitor discharge welding and friction welding.

Description

lightweight valve

The invention is based on a lightweight valve according to the preamble of claim 1, as is known for example from DE 198 04 053 AI. Furthermore, the invention relates to a method for producing such a lightweight valve according to the preamble of claim 5.

The use of weight-optimized valves in internal combustion engines can significantly reduce the loss of friction in the valve train. This is particularly important for high-speed internal combustion engines, but it also plays an important role in alternative valve train systems that are not based on conventional camshaft control. In addition to the use of lightweight materials (such as silicon nitride ceramic, titanium, aluminum alloys or titanium aluminides), the valve weight can be reduced in particular by introducing cavities in the valve stem and / or in the valve cone.

From the generic DE 198 04 053 AI a hollow lightweight valve with a stem, a valve cone and a valve plate is known, the valve cone and valve plate together forming a cavity. The valve cone and valve disc are thin-walled individual parts which are connected to one another and to the valve stem by means of soldering or welding. In order to achieve high strength and rigidity of the valve, in particular in the area of the valve cone, despite the small wall thickness, the cavity of the valve is provided with a support structure which supports the valve plate cover with respect to the stem. This support structure should minimize the deformation of the valve head under load and prevent cracking in the area of the valve head.

In the embodiments of the lightweight valve shown in DE 198 04 053 AI, valve cone and valve plate are connected with fillet welds; The common fusion welding processes such as e.g. TIG, laser or electron beam welding - in question. However, due to the comparatively high heat development, these welding processes can only be used to a limited extent in the case of thin-walled valve geometries, especially when the valve cavity is filled with a metallic cooling medium: Because of the spatially closely spaced arrangement of cooling metal and welding surface, there is in these cases the risk that the cooling metal will melt and reach the welding surface, which can result in a significant reduction in the strength and tightness of the weld. To avoid this problem, the cooling medium can be retrofitted - i.e. be filled after welding; however, this is accompanied by an additional process step of closing the cavity and is therefore very complex. Another disadvantage of the above-mentioned welding processes is that the process times (taking into account the positioning and alignment of the valve plate with respect to the valve plug, a possible subsequent filling of the cooling metal and subsequent closing of the cavity) are uneconomically long. For some material combinations of valve disc and valve cone, e.g. For parts made of titanium-based alloys, a protective gas atmosphere or vacuum is also required when using these welding processes, which further increases the manufacturing outlay and thus the costs of such a lightweight valve.

The invention is therefore based on the object of providing a lightweight valve which, on the one hand, has high stability with respect to the thermal and mechanical operating loads. tion, on the other hand is simple and inexpensive to manufacture. Furthermore, the invention has for its object to provide a large-scale production method for such a lightweight valve.

The object is achieved by the features of claims 1 and 5.

The lightweight valve then consists of a valve body - which in turn comprises the valve stem and the hollow valve cone - and a valve plate cover, which is connected to the valve cone using a press-fit welding process. In the assembled position of the valve, a weight-reducing cavity is formed between the valve cone and the valve plate cover, which cavity is provided with a strengthening support structure.

In contrast to the conventional fusion welding processes, the press-connection welding processes have the advantage that these processes are accompanied by locally limited heating of the welding area. Therefore, negligible warpage of the workpieces occurs when using these methods. In addition, process-reliable welding of the thin-walled valve components is therefore possible without the risk of a weakening of the welding area (for example due to contamination of the welding surface by molten cooling metal). Furthermore, a wide range of different material combinations can be connected without protective gas using these processes. Furthermore, in contrast to fusion welding, there is no "welding path" in the true sense of the word, with which a welding head would have to be guided, in contrast to fusion welding; therefore, using a material-displacing welding process, the rotational symmetry of the valve to be produced can be used, to achieve a very simple - and therefore inexpensive - highly precise relative positioning of the individual parts in the welding device used. Friction welding or a resistance pressure welding process are particularly suitable as welding processes for connecting the valve body to the valve cover.

In friction welding, the heat required for welding the valve plate cover to the valve body is generated by a relative movement of the individual components pressed against one another (see claim 6). For this purpose, for example, the valve body is set in rotation, while the valve plate cover is firmly clamped in an axially displaceable device and is pressed against the rotating valve body. When the temperature and plasticity required for welding are reached, the rotating valve body is braked and, at the same time, the contact pressure is increased, so that the two parts are welded in an annular contact area by compressing the valve body against the valve plate cover. The welding parameters (speed, friction force, braking and upsetting time etc.) depend on the material combination and the geometry of the joining partners in the welding area.

In resistance pressure welding (eg projection welding or capacitor discharge welding), the workpieces to be welded - valve body and valve plate cover - are clamped into the welding device in such a way that the two workpieces touch along an annular contact area. Due to the high currents flowing (for example due to the discharge of a capacitor), the valve body and valve plate are welded to one another in this contact area, so that an annular, continuous connecting web is formed between the two workpieces (see claim 7). Since the welding pulse is very short (approx. 10 to 15 milliseconds for capacitor discharge welding) and since the currents are introduced into a locally narrowly limited area, there is only a slight distortion of the workpiece. In both projection welding and capacitor discharge welding, the quality of the welding result essentially depends on the fact that a continuous ring-shaped contact area is formed between the valve body and the valve disk cover, along which the local material heating and welding takes place. In an embodiment that is particularly easy to manufacture, the valve disk cover blank has a peripheral edge in the edge area on the side facing the valve body, which edge meets a conically shaped area of the valve body in the assembled position with the valve body (see claim 8). In a further embodiment of the invention that is easy to manufacture, the valve disk cover blank is provided with a frusto-conical edge region, while the valve body blank has an edge in the contact area of the valve disk cover blank between a hollow cylindrical and a planar section (see claim 9). In both cases, an annular edge meets a conically shaped counter region, whereby a high-strength annular weld is achieved.

Advantageously, a one-piece valve body blank (comprising a valve stem and a valve cone) is used to manufacture the lightweight valve (see claim 2). This has the advantage that no additional process step for connecting the valve stem to the valve cone is necessary to produce the valve body blank; furthermore, in the case of one-piece valve bodies, there is no risk of a reduction in strength due to an incorrect connection of the individual parts.

In an advantageous embodiment of the invention, the cavity between the valve plug and the valve plate cover is filled with a cooling medium, by means of which the heat dissipation from the thermally highly stressed areas of the valve plate cover and the zones of the valve plug adjacent to it is improved (see claim 3). As a cooling medium in particular Sodium used. Here, the good thermal conductivity of sodium is used, but in particular the transport of heat by the shaking movement of the valve during operation, whereby hot sodium is transported to cooler areas, where it emits heat and is then available again for cooling in the hotter plate area. Instead of sodium, other metals with a low melting point, such as potassium or sodium-potassium alloys, can also be used.

It is particularly advantageous to extend the cavity inside the valve into the valve stem (see claim 4). This offers great advantages in particular if the cavity is filled with a cooling medium, since in this case the shaking movement of the valve allows the cooling medium to be transported from the hot area of the valve plate into the cooler inside of the shaft, where - due to the larger temperature difference - it is particularly effective Experiences cooling.

The invention is explained in more detail below with reference to several exemplary embodiments illustrated in the drawings; show:

Fig. La an inventive lightweight valve;

Fig. Lb an alternative embodiment of the invention

Lightweight valve;

Fig. 2 is a schematic representation of the process steps in the manufacture of the lightweight valve of Figure la: valve body blank and valve plate cover blank ...

Fig. 2a ... before welding; Fig. 2b ... during welding Fig. 2c ... in the fully welded state. Fig. 3 shows an alternative embodiment of the blanks to be welded.

Figure la shows a schematic representation of a lightweight valve 1 according to the invention, consisting of a valve body 2 and a valve plate cover 3, which are welded together by means of a press-connection welding method. The valve body 2 in turn consists of a valve stem 4 and a hollow valve cone 5 and is formed in one piece in the present exemplary embodiment. Valve cone 5 and valve plate cover 3 together form the so-called valve head 6. A weight-optimizing cavity 7 is formed between the valve cone 5 and the valve plate cover 3. A support structure 8 arranged in the cavity 7 supports the valve plate cover 3 with respect to the shaft 4; in the present case, the support structure 8 is formed by a pin 9 arranged centrally in the cavity 7. Instead of the one-piece valve body 2 shown in FIG. 1, a valve body composed of several individual parts (e.g. using different materials for the stem and valve cone) can also be used.

The valve plate cover 3 can, according to the invention, be welded to the valve cone 5, for example with the aid of capacitor discharge welding. The associated method steps are shown schematically in FIGS. 2a to 2c. In this case, a valve body blank 10 is assumed, which - as shown in FIG. 2a - is provided with an inner cavity 11 in the region of the valve cone 5. In the interior 11 of the valve cone 5, a support structure 8 is provided, which projects a predetermined depth into the interior 11. A conically shaped joining region 13 is provided on the wall 12 of the inner cavity 11. The valve body blank 10 can be produced by forming (forging, extrusion, etc.) and / or by machining. - A valve plate cover blank 14 is used as joining partner, which in the present example has the shape of a cylindrical disk 15; the joining area 16 provided on the valve disk cover blank 14 thus has the shape of an annular peripheral edge 17 with a rectangular contour.

To weld the two joining partners 10, 14, the valve plate cover blank 14 is inserted into the cavity 11 of the valve body blank 10; the circumferential edge 17 of the valve disk cover blank 14 lies linearly on the conical joining area 13 in the inner cavity 11 of the valve cone 5. Then, with the aid of a capacitor discharge welding device 18 (indicated schematically by dashed lines in FIG. 2b), the valve plate blank 14 is pressed into the interior 11 of the valve body blank 10 (arrow 19 in FIG. 2b) and at the same time the capacitor integrated in the circuit of the welding device 18 is discharged ; Due to the high currents flowing through the joining partners 10, 14, the edge 17 welds to the joining area 13 opposite it on the valve body blank 10, so that an annular, continuous connecting web 20 is formed between the valve plate cover blank 14 and valve body blank 10 and the cavity 7 formed between the two joining partners 10, 14 is sealed off from the outside world. Since the welding pulse during capacitor discharge welding is very short at 10-15 milliseconds, there is only a slight delay in the joining partners 10, 14. The flat underside of the valve disk cover blank 14 ensures a large contact surface 21 with the welding stamp 22 of the capacitor discharge welding device 18. This contact surface 21 is parallel to the annular edge 17, which means that the entire edge 17 is pressed onto the opposite joining surface 13 of the joint in a precisely directed and uniform manner Valve body blanks 10 allowed. Since the contact surface 21 is substantially larger than the (approximately linear) contact surface of the edge 17 on the joining area 13 of the valve body blank 10, it is ensured that the material heating and plasticizing takes place reliably on the edge 17 during welding. The cone angle 23 of the conical joining area 13 is preferably between 10 ° and 80 °. The diameter of the disk 15 is matched to the diameter and the cone angle 23 of the joining area 13 and the welding parameters (current intensity, contact pressure etc.) are selected so that the valve plate blank 14 penetrates so deep into the inner cavity 11 during welding that it rests on the support structure 8; this ensures that the valve plate cover 3 is supported in later operation by the support structure 8 with respect to the valve stem 4.

A wide range of different materials can be welded by means of capacitor discharge welding, so that the material of the valve body 10.2 and valve plate cover 14.3 can be selected according to the other requirements (e.g. on the functional side). In particular, all known valve materials and e.g. Titanium aluminides, iron aluminides, metal matrix composites, titanium and aluminum alloys etc. are used and combined with one another. The method can therefore also be used in particular for applications for which other welding methods cannot be used or can only be used with difficulty.

An alternative embodiment of the joining areas 13 ', 16' on the valve body blank 10 'and the valve plate cover blank 14' is shown in FIG. 3: In this case, the joining area 16 'on the valve plate blank 14' has the shape of a truncated cone while on a circumferential edge 13 'is provided for the valve body blank 10'. Analogous to the example in FIGS. 2a and 2b, the contact area between the two blanks 10 ', 14' is also given here by an annular circumferential line contour. In addition to the exemplary embodiments of the joining partners 10, 14 shown in FIGS. 2a and 3, any further geometric configurations are possible; it must be ensured that the two joining Touch the partner in the assembled position in a ring-shaped, linear contact area.

As an alternative to capacitor discharge welding, the two joining partners can be joined by projection welding, the peripheral edge 17, 13 'on the valve body blank 10, 10' or valve plate cover blank 14, 14 'acting as an ignition initiating projection.

Furthermore, the two joining partners can be connected to one another by friction welding. In this case e.g. the valve disk cover blank 14 is held in the friction welding machine in a torsionally fixed but axially movable manner, while the valve body blank 10 is mounted and driven in a stationary, rotating manner. First, the blanking valve cover blank 14 is pressed against the conical joining surface 13 of the valve cone 5 with an initially moderate axial force, the material of both parts lying near the contact zone heating up due to friction and thereby softening. If a temperature suitable for welding and a doughy state is reached in the contact zone of the parts, the rotating valve body blank 10 is shut down very quickly and at the same time the axial force of the valve disk cover blank 14 is increased and this is moved by a certain axial stroke into the inner cavity 11 of the valve cone 5 pressed in. The parts 10, 14 weld intimately to one another at the contact zone. - In contrast to projection and capacitor discharge welding, the contact surface between the two joining partners 10, 14 does not have to be linear when using friction welding; rather, depending on the wall thickness and the geometry of the joining partners 10, 14 in the joining area, it may be expedient to provide a two-dimensional contact zone.

After the joining partners 10, 14 have been welded, the valve 1 is machined; Here, an area of the valve disk cover blank 14 protruding from the valve cone 5 is cut to the desired dimension (dashed line 24 in FIG. 2c). wear and remove any remaining burrs etc.

An alternative embodiment of a lightweight valve 1 'according to the invention is shown in FIG. 1b: In this case, the cavity 7' extends into the valve stem 4 '. In this exemplary embodiment, the support structure 8 is formed by a plurality of pins 9 ′, which are arranged equidistantly on a circular arc. The cavity 7 'is filled with a cooling medium 25 (e.g. sodium), which is in the liquid state at the usual operating temperatures of the valve 1'. During operation of the valve 1 ', the cooling medium 25 therefore flows through the cavity 7' and thus supports the removal of heat from the hot area of the valve head 6 'into the cooler stem area 4'. To produce the valve 1 'of FIG. 1b, the interior 11 of the valve body blank 10, 10' is first filled with cooling medium 25 and then - using one of the methods described above - welded to the valve plate cover blank 14, 14 '. For welding, the cooling medium is either pressed into the interior 11 of the valve body 10, 10 'in a solid state of aggregation and held there in position by the support structure 8, and / or the valve body blank 10, 10' is connected to the one contained in its interior 11 ( liquid or solid) cooling medium 25 vertically aligned during welding in such a way that the cooling medium 25 cannot flow out.

As an alternative to or in addition to the pins 9, 9 'shown in FIGS. 1 a and 1 b, the inner support structure 8 can also have annular support walls and / or laterally projecting support ribs. The wall thickness of the valve cone 5 or the valve plate cover 3 can be optimized in a targeted manner, taking into account the design of the support structure 8, in order to further reduce the weight of the valve 1, 1 '.

.oOo.

Claims

claims

1. Lightweight valve, in particular for an internal combustion engine, with a valve body comprising a valve stem and a valve cone and a valve plate cover, wherein the valve cone and valve plate cover together form a cavity and wherein a support structure is provided in this cavity for supporting the valve plate cover with respect to the valve stem, characterized in that the valve plate cover (3) is connected to the valve cone (5,5 ') by means of a press-connection welding process.

2. Lightweight valve according to claim 1, so that the valve body (2, 2 ') is formed in one piece.

3. Lightweight valve according to claim 1 or 2, so that the cavity (7, 7 ') of the valve (1, 1') is filled with a cooling medium (25), in particular with sodium.

4. Lightweight valve according to one of the preceding claims, that the cavity (7 ') extends into the valve stem (4).

5. Method for producing a lightweight valve, especially for an internal combustion engine,

a valve body blank, which surrounds a valve stem and a partially hollow valve cone. summarizes, is welded to a valve plate cover blank, characterized in that a press-connection welding process is used as the welding process.

6. The method according to claim 5, d a d u r c h g e k e n n z e i c h n e t that the friction welding is used as a welding process.

7. The method as claimed in claim 5, so that a resistance pressure welding method, in particular projection welding or capacitor discharge welding, is used as the welding method.

8. The method according to any one of claims 5 to 7, characterized in that for connecting the valve body blank (10) with the valve plate cover blank (14) with an edge (17) provided joining area (16) of the valve plate cover blank (14) is welded with a sectionally conical wall (13) of the interior (11) of the valve body blank (10).

9. The method according to any one of claims 5 to 7, characterized in that for connecting the valve body blank (10 ') with the valve plate cover blank (14') a frusto-conical edge region (17 ') of the valve plate cover blank (14') with a linear edge (13 ') of the valve body blank (10') delimiting the interior (11) is welded.

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