WO2007137314A2

WO2007137314A2 - Cylinder head for an internal combustion engine

Info

Publication number: WO2007137314A2
Application number: PCT/AT2007/000248
Authority: WO
Inventors: Robert Roithinger; Franz Langmayr; Michael Howlett
Original assignee: Avl List Gmbh
Priority date: 2006-05-26
Filing date: 2007-05-24
Publication date: 2007-12-06
Also published as: JP5186490B2; EP2024116A2; ATE531466T1; JP2009538396A; WO2007137314A3; EP2024116B1

Abstract

The invention relates to a lightweight cylinder head (1) for an internal combustion engine, comprising at least one cast piece (4) that is cast into an external structure (2), the external structure (2) and the cast piece (4) being made of different materials. In order to obtain high resistance to vibration and to temperature variations, at least one cast piece (4) forms a support structure (3) and embodies at least one screw stud (5) for receiving a cylinder head screw.

Description

Cylinder head for an internal combustion engine

The invention relates to a cylinder head for an internal combustion engine in lightweight construction with at least one infused into an external structure sprue, said outer structure and sprue made of different materials. Furthermore, the invention relates to a cylinder head made of gray cast iron for a reciprocating engine, in particular an internal combustion engine, with at least one opening into a combustion chamber opening for a gas exchange channel which can be closed by a lifting valve, wherein the lifting valve rests in the closed state on a valve seat formed by the cylinder head. Furthermore, the invention relates to a method for producing this cylinder head.

The increasing power density, especially of passenger car diesel cylinder heads is limited by the fatigue strength and the thermal cycling stability of the cylinder head. Due to the increasing peak pressures, in particular in the area of the water jacket and the gas exchange channels, there is a lack of vibration resistance resulting in vibration breaks. The thermal entry into the cylinder head is an approximately constant part of the power. As a result, the amplitudes of the surface temperatures increase at least proportionally to the power density, resulting in insufficient thermal cycling resistance to damage the cylinder head in each thermal cycle.

A high fatigue strength can be realized by cylinder heads of gray cast iron, in particular of GJV (cast iron with vermicular graphite). Switching from aluminum alloys to gray cast iron leads to an increase in the fatigue strength in critical zones by about 50%. The disadvantage of cast iron cylinder heads, however, is the poorer thermal conductivity, which is worse by about a factor of 5, than with Al-Si-Mg alloys. This leads to higher maximum temperatures for cast iron heads (about 400 ⁰ C). This temperature level is already reached at moderate power densities. Increasing temperature load due to higher power density would lead to a strong decrease in the strength and thus the service life due to thermo-mechanical cracking. In addition, the geometric conditions of relatively close-packed engines in passenger cars lead to a massive decrease in life under thermal load alternately.

The requirements for fatigue strength and rigidity would therefore speak for a cylinder head made of steel or cast iron, the requirements for the thermal alternating resistances rather for an aluminum cylinder head. It is already known to produce cylinder heads made of composite materials.

EP 0 262 240 A1 describes a cylinder head which has a bottom plate and a separately manufactured upper part, which are releasably connected to one another. The bottom plate consists of a material with higher high-temperature strength and lower thermal conductivity than the upper part. The disadvantage is that the composite zone is formed in a highly loaded area, and that a poor heat transfer through the bottom plate takes place, resulting in a high thermal cycling during power cycling with appropriate material damage and high component temperatures on the gas side.

From EP 0 462 850 Al it is known to pour in a cylinder head a fiber-reinforced insert between the valve openings to increase the wall strength. There may be problems with bonding in the transition zone. Another disadvantage is that the lower thermal conductivity leads to increasing temperature amplitudes. In addition, composite materials have a strong tendency to embrittle, which greatly reduces life under thermal cycling.

DE 31 00 755 A1 describes a cylinder head for an internal combustion engine, which has a reinforcement with one or more inserts of dispersion-hardened sintered aluminum between the valve webs. However, the bonding of the aluminum sintered part in the casting process is very difficult because the transition region is located in a thermally and mechanically highly stressed zone. The long-term strength properties can not be improved with the measures mentioned.

It is known to produce a valve seat for a cylinder head of an internal combustion engine to fuse a filler material by introducing energy at that point with the cylinder head on which the valve seat is to be formed. Such valve seats and processes for their preparation are known from publications WO 2004/048756 A1, DE 199 12 889 A1, DE 103 29 912 B4 or WO 99/02839 A1. Furthermore, DE 102 18 563 A1 discloses a method for producing valve seats using a laser plating process.

Furthermore, it is known to change the structure of metallic cast materials by local melting operations to increase the wear resistance.

Melting processes are relatively complicated and cost-intensive, since a different wear-resistant material from the cast structure has to be applied. Furthermore, it is known to inductively harden valve seats. The disadvantage, however, is that the structure of inductively hardened seats at higher temperatures, as can be achieved for example on exhaust valves of supercharged internal combustion engines, is not sufficiently stable.

The object of the invention is to avoid these disadvantages and to provide a cylinder head which has high fatigue strength and high thermal cycling stability. Another object of the invention is to produce stable and wear-resistant valve seats in a cylinder head of the type mentioned in the simplest possible way.

According to the invention this is achieved in that the sprue forms a support structure and at least forms a screw neck for receiving a cylinder head bolts. Preferably, the sprue per cylinder has at least one preferably central insert, which can serve for receiving a component opening into the combustion chamber.

To increase the fatigue strength, it is advantageous if at least two Schraubenbutzen are connected to each other via at least one preferably normal to the Butzenachsen arranged second brace, wherein the Schraubenbutzen and / or the insert may be formed as a cylindrical sleeve. The central insert is not formed to the gas side of the fire deck, so as not to adversely affect the heat conduction there. Rather, between the insert and the gas side is a region of the outer structure, wherein the insert is embedded in the outer structure. The cylindrical insert takes on - depending on the engine type - a spark plug or an injector. The shape of the insert is designed according to the intended application. If the insert is designed to accommodate an injector, then it is advantageous if a slug for receiving a screw of an injector screw connection is cast onto the insert. The slug thus absorbs the screw-in hole for a clamping screw of the injector screw connection. Thus, a problem zone is defused on the cylinder head, since the required clamping forces for aluminum materials are critically high.

The sprue consists of a truss-like frame, which is formed by the screw heads for the cylinder head bolts and in which the central insert is integrated via the oblique second braces. The first struts between the screw-trimmings prevent the structure in the upper deck from stretching and thus causing a cyclical bend on the gas deck. The central cylinder formed by the insert therefore acts as a stabilizing column. The first and second braces support the gas exchange channels. In an advantageous embodiment of the invention it is provided that the Schraubenbutzen each cylinder in the fire deck are connected by a preferably annular third brace with each other, particularly preferably the third brace - viewed in plan view - is arranged in the region of the cylinder head gasket. The contour of the third strut retraces the cylinder head gasket to increase its sealing effect.

In a further embodiment of the invention it can be provided that the sprue piece forms at least one receptacle for a valve guide of a gas exchange valve, wherein preferably the receptacle is connected to the screw neck or the insert, wherein a support for a valve spring can be integrated into the receptacle. It can be provided that at least one receptacle for a valve guide of the gas exchange valve is integrated into a conical first or second strut.

It is particularly advantageous if the sprue is designed in several parts and preferably has one cylinder element per cylinder, wherein cylinder elements of adjacent cylinders can preferably be connected to one another via plug connections. Preferably, each cylinder element has two bolt trims connected to one another via a first strut, and in each case a further first strut per screw strut, the two further first struts being connectable to the screw struts of an adjacent cylinder element, preferably attachable to the screw struts. Furthermore, it can be provided that the casting per cylinder has an annular third strut, wherein the annular third strut connectable to the screw neck of the respective cylinder, preferably attachable to the screw neck, is. Furthermore, it can be provided that the third strut of at least one cylinder can be plugged onto the screw neck of the cylinder. These measures facilitate the insertion of the sprue in the chill casting mold.

The outer structure may be made of a light metal, for example of an aluminum alloy, or of a copper alloy. This ensures that the cylinder head on the fire deck side has the highest possible thermal conductivity and is designed so that the thermal cycling induces the lowest possible voltages.

In order to enable a high alternating strength of the cylinder head, it is provided that the sprue made of steel or gray cast iron, preferably with nodular graphite. In contrast to the external structure, the support structure formed by the sprue consists of a material which has a high elasticity. tätsmodul has to ensure a low level of deformation. The high alternating strength is necessary to resist the cyclic gas loads. The use of steel or pre-cast high strength gray cast iron with nodular graphite meets these requirements. The support structure is pre-cast per cylinder and placed with the cores in a chill mold and poured. The support structure has the shape of a framework whose form is based on the needs of the gas exchange channels. It is conceivable to co-infuse the valve seat rings, also screw pipes or the camshaft bearings can be integrated. In addition, support for the injector support can be realized. A simple and positionally accurate arrangement in the chill casting mold is possible when the sprue is made in several parts, with individual parts such as screw, use, recording and / or bracing by plug connections are connected to each other.

To produce stable and wear-resistant valve seats, it is provided that the cast structure is remelted in the region of the valve seat. It is not added material, but only the original cast structure remelted.

To reduce the risk of cracking and the tendency to warp, it is advantageous if the component is preheated before the remelting to a temperature above the martensite start temperature (about 300 ⁰ C) of the casting material. The remelting process is preferably carried out in a laser remelting process.

In the remelting zone, a ledeburitic microstructure is formed from the melt by rapid cooling. The solidification is essentially defined by the high heat conduction from the melt into the base material. The solidification front therefore moves from the melting boundary in the direction of the component surface, whereby the directional structure of the Ledeburit arises. Furthermore, the solidification front transports defects to the surface. These are eliminated with the finishing.

In order to be able to compensate for the deformation and surface wavinesses that occur during remelting, an addition must be taken into consideration, which is then processed together with the valve guide after remelting, for example.

In contrast to known reflow processes, no material is supplied in the process according to the invention, but only the cast structure is remelted. The valve seat thus consists of the cast iron base material of the cylinder head. The remelting process thus achieves a wear-resistant structure of the valve seat without the need to press in a valve seat ring. As a result, a radial press fit is avoided, resulting in a better heat dissipation in the region of the valve seat and it saves installation space and manufacturing costs.

In comparison with inductively hardened valve seats, the remelted structure remains stable even at temperatures that are achieved, for example, on exhaust valves of turbocharged engines.

The invention will be explained in more detail below with reference to FIGS. Show it:

1 shows a cylinder head according to the invention in a first oblique view;

2 shows the cylinder head in a combustion chamber side oblique view from above.

3 shows the cylinder head from the side of the combustion chamber.

4 shows the cylinder head from above;

5 shows the sprue in a side view;

6 shows the sprue in an oblique view;

7 shows the sprue in a plan view;

8 shows a cylindrical element of the sprue in an oblique view;

9 shows this cylinder element in a side view;

10 shows the cylinder element in a further side view;

FIG. 11 shows an end part of the sprue piece in an oblique view; FIG.

Fig. 12 is a third strut in an oblique view;

FIG. 13 shows the valve seat region of a cylinder head in section after machining; FIG. and

Fig. 14 this valve seat area after the remelting before finishing.

The cylinder head 1 for a plurality of cylinders has an outer structure 2 of a light metal, for example, an aluminum alloy or a copper alloy into which a casting 4 forming a support structure 3 is embedded. The support structure 3 is shaped like a truss and consists of steel or gray cast iron. The sprue 4 forms Schraubenbutzen 5 for cylinder head bolts, inserts 6 for receiving injectors or spark plugs, and recordings 7 for valve guides. The Schraubenbutzen 5 are connected to each other via normal to the Butzenachsen 5a first stiffeners 8. Second struts 9 connect the screw 5 with the insert 6. These second struts 9 are inclined at an angle α <90 °, preferably <60 ° to the slug axes 5a and the insert shaft 6a and extend from the screw 5 starting in the direction of the fire deck 17 to the inserts 6. In the exemplary embodiment, the obliquely inclined in the direction of the fire deck second struts 9 also recordings 10 for valve guides. At each insert 6 a slug 16 is cast, the. has a screw 16a for a clamping screw of a Injektorverschraubung.

Furthermore, in the region of the fire deck 17, the respective contour of the cylinder head gasket formed annular third struts 11 are provided, which connect the screw 5 with each other.

The sprue 4 in the exemplary embodiment per cylinder 20 consists of a cylinder element 19, and an annular third strut 11 in the region of the fire deck 17. These two castings per cylinder 20 are inserted into each other by periodic continuation of the gate 4. In addition, is as a conclusion of the cylinder head end a consisting of two Schraubenbutzen 5 and a first strut 8 existing end piece 21, which is shown in Fig. 11.

Each cylinder element 19 consists of at least two screw 5 and _. At least three first struts 8. Furthermore, the cylinder element 19 can have an insert 6 and second struts 9, as shown in FIGS. 9 to 14. The first and third struts 8, 11 have annular eyelets 12, 13, in which the screw 5 are inserted. By inserting the eyelets 12 on the screw 5 also cylinder elements 19 of a plurality of cylinders 20 can be connected to each other.

As can be seen from FIGS. 8 and 10, a first strut 8 per cylinder can be connected to the slug 16 of the insert 6 via the web 8a. The cylinder head 1 is made by the outer structure 2 on the side of the fire deck 17 of a material with the highest possible thermal conductivity and is designed so that the thermal cycling induced as low as possible voltages. The material of the outer structure 2 is, for example, an aluminum alloy or a copper alloy. The sprue 4 within the outer structure 2, however, consists of a material which has such a high modulus of elasticity to ensure a low level of deformation. Furthermore, the sprue 4 should also have a high alternating strength in order to resist the cyclic gas load. As a material for the gate 4 thus offers high-strength gray cast iron with nodular graphite (GJS) or steel. In this case, a support structure 3 per cylinder is pre-cast and placed with the cores for the gas exchange channels in the chill mold and cast. The plug-in system of the support structure 4 shown in FIGS. 9 to 14 facilitates insertion into the chill casting mold.

The gas side of the cylinder head 1 can be designed as a spherical cap as part of the design possibilities of Ventilverkippung. The aluminum alloy of the outer structure 2 has a high thermal conductivity. It has the necessary structural properties without heat treatment, which is to be avoided because of the pouring solution. Therefore, it is ideally low-alloyed aluminum with as homogeneous a structure as possible without internal notches and with the highest possible elongation at break.

The existing of steel or nodular casting 4 has the shape of a framework whose form is based on the needs of the gas exchange channels. It is possible to co-pour the valve seat rings. Screw pipes can also be integrated. Furthermore, support for the injector support can be integrated into the sprue 4.

The combination of outer structure 2 and support structure 3 fulfills the extreme requirements occurring at different locations primarily by the appropriate choice of materials and by a corresponding shaping of the support structure 3, or the combustion chamber boundaries. It is therefore much better suited to endure extreme loads than homogeneous cast iron components, which can not stand the thermal stress or aluminum alloys, which are not at a sufficient level with the rigidity and fatigue strength.

The cylinder head 101 of gray cast iron illustrated in FIGS. 13 and 14 for a reciprocating piston engine, for example an internal combustion engine, has at least one gas exchange opening 102 opening into a combustion chamber 108 for a gas exchange duct 103, which can be opened by a lift valve 104. The lift valve 104 is seated in the closed state on a valve seat 105 formed by the cylinder head 101 itself. The valve seat 105 is hardened by a local laser remelting process, wherein the cast structure 106 is brought to the melting point in the region of the valve seat 105. Before the actual remelting process, the cylinder head 101 is heated to a preheating temperature (about 300 ^° C.) of the respective material in order to reduce the tendency to distort, as well as to reduce the risk of cracking. Rapid cooling produces a ledeburitic microstructure in the remelting zone from the melt. This results in the valve seat region 105 is a defect-free, finely structured remelt layer with high hardness (500-600 Hv 5) and good ductility, which has a high resistance to wear and fatigue.

In order to be able to compensate for the deformation occurring during remelting, as well as waviness, an addition 107 has to be taken into account, which is then processed together with the valve guide after remelting, for example.

Claims

PATENT CLAIMS

Cylinder head (1) for an internal combustion engine in lightweight construction with at least one in an outer structure (2) cast infusion (4), wherein the outer structure (2) and sprue (4) made of different materials, characterized in that at least one sprue (4 ) forms a support structure (3) and at least one Schraubenbut- zen (5) for receiving a cylinder head screw is formed.

2. Cylinder head (1) according to claim 1, characterized in that the sprue (4) per cylinder (20) forms at least one preferably central insert (6) for receiving a component opening into the combustion chamber.

3. Cylinder head (1) according to claim 1 or 2, characterized in that at least two Schraubenbutzen (5) are connected to each other via at least one preferably normal to the Butzenachsen (5a) arranged first strut (8).

4. Cylinder head (1) according to claim 2 or 3, characterized in that at least one Schraubenbutzen (5) with the insert (6) via at least a second strut (9) is connected, wherein preferably the strut with the Butzenachse (5a) and the insert shaft (6a) encloses an angle (α) <90 °, preferably <60 °.

5. Cylinder head (1) according to one of claims 1 to 4, characterized in that the screw neck (5) and / or the insert (6) is designed as a cylindrical sleeve.

6. Cylinder head (1) according to one of claims 2 to 5, characterized in that the insert (6) from the gas side of the fire deck (17) through the outer structure (2) is separated.

7. Cylinder head (1) according to one of claims 2 to 6, characterized in that on the insert (6) has a slit (16) is cast for receiving a screw of a Injektorverschraubung.

8. Cylinder head (1) according to one of claims 1 to 7, characterized in that the Schraubenbutzen (5) of each cylinder (20) in the region of the fire deck (17) by a preferably annular third brace (11) are interconnected, with particular preference the third brace (11) - in plan view - in the area of the cylinder head is arranged seal and substantially the contour of the cylinder head gasket is reformed.

9. Cylinder head (1) according to one of claims 1 to 8, characterized in that the Eingussstück (4) at least one receptacle (10) for a valve guide of a gas exchange valve is formed, wherein preferably the receptacle (10) with the Schraubenbutzen (5) or the insert (6) is connected.

10. Cylinder head (1) according to one of claims 1 to 9, characterized in that a support for a valve spring of the gas exchange valve in the receptacle (10) is integrated.

11. Cylinder head (1) according to one of claims 1 to 10, characterized in that at least one receptacle (10) for a valve guide in the first or second strut (8, 9) is integrated.

12. Cylinder head (1) according to one of claims 1 to 11, characterized in that the sprue (4) is designed in several parts and preferably has a cylinder element (19) per cylinder (20).

13. Cylinder head (1) according to claim 12, characterized in that cylinder elements (19) of adjacent cylinders (20) are preferably connectable to one another via plug connections.

14. Cylinder head (1) according to claim 12 or 13, characterized in that each cylinder element (19) two via a first strut (8) interconnected Schraubenbutzen (5), and per Schraubenbutzen (5) each have a further first strut (8). wherein the two other first struts (8) with the Schraubenbutzen (5) of an adjacent cylinder element (19) connectable, preferably on the Schraubenbutzen (5) attachable, are.

15. Cylinder head (1) according to one of claims 12 to 14, characterized in that the third strut (8) at least one cylinder (20) on the screw neck (5) of the cylinder (20) can be plugged.

16. Cylinder head (1) according to one of claims 1 to 15, characterized in that the outer structure (2) consists of a light metal alloy, preferably an aluminum alloy, or a copper alloy.

17. Cylinder head (1) according to one of claims 1 to 16, characterized in that the Eingussstück (4) made of Stahlt or gray cast iron, preferably with nodular graphite. - 2 -

18. Cylinder head (1) according to one of claims 1 to 17, characterized in that the sprue (4) has the shape of a truss.

19. Cylinder head (101) made of cast iron for a reciprocating engine, in particular an internal combustion engine, with at least one opening into a combustion chamber (108) opening (102) for a gas exchange channel (103) which is closable by a lift valve (104), wherein the lift valve (104) in the closed state rests on a valve seat (105) formed by the cylinder head (101), characterized in that the cast structure (106) is hardened in the region of the valve seat (105) by a remelting process, preferably by a laser remelting process ,

20. A method for producing a cylinder head (101) according to claim 19, characterized in that the cast structure (106) in the region of the valve seat (105) is remelted.

21. The method according to claim 20, characterized in that the cast structure (106) is preheated prior to the remelting process to a preheating temperature, wherein preferably the preheating temperature is above the martensite start temperature of the casting material of the cylinder head (101).

22. The method according to claim 20 or 21, characterized in that the remelting of the cast structure (106) by a laser remelting process takes place.

23. The method according to any one of claims 20 to 22, characterized in that the remelted cast structure (106) is accelerated cooled, so that a ledeburitic structure is formed.