WO2012112084A1

WO2012112084A1 - Cylinder head cooling insert

Info

Publication number: WO2012112084A1
Application number: PCT/SE2011/000028
Authority: WO
Inventors: Thomas SVANBERG; Lars PAGIL; Claes Kuylenstierna
Original assignee: Volvo Lastvagnar Ab
Priority date: 2011-02-17
Filing date: 2011-02-17
Publication date: 2012-08-23

Abstract

Cylinder head for a combustion engine, comprising at least one inlet valve opening, at least one exhaust valve opening, at least one injector opening and at least one cooling channel, where the cylinder head further comprises at least one insert in the fireface wall extending from the fireface of the cylinder head into the cooling channel of the cylinder head, where the insert is made of a material having a higher thermal conductivity than the cylinder head material. The advantage of the invention is that the cooling of the fireface is improved, which in turn will improve the high cycle fatigue strength and the low cycle fatigue strength.

Description

CYLINDER HEAD COOLING INSERT

TECHNICAL FIELD

The present invention relates to an arrangement for cooling the combustion side of a cylinder head of an internal combustion engine. The inventive arrangement is specifically suitable for larger engines, such as larger diesel engines.

BACKGROUND ART

The combustion chamber of a modern engine is subjected to very high pressures and temperatures during combustion. The high pressure and high temperature puts high mechanical stress on the material. Especially the material of the cylinder head is thus subjected to high mechanical stress due partly to temperature gradients. This problem is mainly located to the areas around the inlet and outlet valves, where the material is heated differently and particularly cooled in a non-symmetric way, since the area around the inlet valve or inlet valves will be cooled some each time the inlet valve opens to let in fresh air for the combustion. The area around the fuel injector will also be cooled some by the fuel being injected. Also the outer border of the combustion chamber on the cylinder head will have a lower temperature due to the cooling system of the engine. Such temperature gradients will occur when the engine is in use, i.e. during combustion. The problem is concentrated to the central area of the cylinder head where the fuel is injected and where the fuel ignites. This area is referred to as the cylinder head fireface.

Further stress will be imposed on the cylinder head when the engine is started and when the engine is stopped. In these cases, the warming up and cooling down of the cylinder head will also impose mechanical stress on the cylinder head. On larger engines, the problem may be greater due to more material to heat up and cool down. This mechanical stress may lead to cracks forming in the material. These cracks may propagate through the material until the material breaks.

It has been proposed to introduce different inserts in the cylinder head material, mainly around the inlet and outlet valve regions, in order to prevent and control the forming of cracks in the material. Some of these inserts will form a type of expansion joints formed by integrally cast inserts, where the inserts fill the expansion joint.

FR 2654775 discloses a cylinder head for an internal combustion engine having at least one insert cast in between two valve seats. The insert has a profile which changes progressively from one end of minimum width, flush with the hot surface side of the combustion chamber to a rounded end shape. The insert may include an internal zone without metal. This type of insert is intended to limit the risks of thermal cracks appearing in diesel engines. FR 2883043, FR2736967, DE 3524776, DE 3405904 and DE 1294093 also describe various types of inserts arranged in the face of the cylinder head to prevent crack formation.

These arrangements may work in specific cases. There is however still room for improvements. DISCLOSURE OF INVENTION

An object of the invention is therefore to provide an arrangement for cooling the combustion side of a cylinder head. A further object of the invention is to provide an arrangement that will minimize crack susceptibility of a cylinder head. The solution to the problem according to the invention is described in the characterizing part of claim 1. An inventive method for improving the cooling of a cylinder head is described in claim 11. The other claims contain advantageous further developments of the inventive arrangement and method.

In a cylinder head for a combustion engine, comprising at least one inlet valve opening, at least one exhaust valve opening, at least one injector opening and at least one cooling channel, the object of the invention is achieved in that the cylinder head further comprises at least one insert in the fireface wall extending from the fireface of the cylinder head into the cooling channel of the cylinder head, where the insert is made of a material having a higher thermal conductivity than the cylinder head material.

By this first embodiment of the cylinder head according to the invention, a cylinder head with improved cooling of the fireface is obtained. This will in turn improve the high cycle fatigue strength and the low cycle fatigue strength of the cylinder head. This is of great importance since the working pressure and also working temperature of modern engines is higher than previous.

In an advantageous development of the inventive cylinder head, the inserts are mounted in the cylinder head after the cylinder head is cast. In this way, the precision of the mounting position can be improved which will improve the high cycle fatigue strength and the low cycle fatigue strength of the cylinder head further. Another advantage of this is that materials having a lower melting temperature than the material of the cylinder head can be used for the inserts. Suitable materials for the inserts are aluminium or copper, where aluminium has a lower melting temperature than cast iron, which is mostly used for cylinder heads. Different alloys comprising aluminium and/or copper are also suitable for the inserts.

In an advantageous development of the inventive cylinder head, the inserts are tapered towards the cooling channel. In this way, the inserts can easily be mounted in a gas tight way in the cylinder head. BRIEF DESCRIPTION OF DRAWINGS

The invention will be described in greater detail in the following, with reference to the attached drawings, in which

Fig. 1 shows a cut view through a cylinder head according to the invention,

Fig. 2 shows a view from the combustion side of the cylinder head according to the invention,

Fig. 3 shows a cut view through a cooling channel with inserts projecting into the cooling channel of the cylinder head according to the invention, and

Fig. 4 shows an alternative shape of the inserts of the cylinder head according to the invention.

MODES FOR CARRYING OUT THE INVENTION

The embodiments of the invention with further developments described in the following are to be regarded only as examples and are in no way to limit the scope of the protection provided by the patent claims.

Fig. 1 shows a .cut view through a part of a cylinder head 1 according to the invention. Fig. 2 shows a view from the combustion side of the cylinder head. Fig. 3 shows a cut view through a cooling channel with inserts projecting into the cooling channel. Fig. 1 is cut along line A - A shown in Fig. 2 and Fig. 3 is cut along line B - B shown in Fig. 1.

In the engine used as an example, the injector is positioned such that the injector opening 3 is positioned in the centre of the fireface 12 of the cylinder head. The surface of the cylinder head directed towards the combustion chamber is referred to as the fireface. The wall holding the fireface, i.e. the part of the cylinder head that is directed towards the combustion chamber, is referred to as the fireface wall 13. As can be seen in Fig. 2, the fireface wall is provided with four valves positioned around the injector 2 in a symmetric way, two inlet valves 4, 5 and two exhaust valves 6, 7. The valves are in turn positioned in four valve openings, two inlet valve openings 8, 9 and two exhaust valve openings 10, 11 having valve seats. In the cylinder head, there is a plurality of cooling channels in which a cooling fluid, usually a water mixture, flows. The cooling channel 14 that delimits the fireface wall is shown.

The cylinder head is adapted to seal the top of the combustion chamber and is mounted on the cylinder block. Depending on the type and size of the engine, the cylinder head may be either a single stand-alone cylinder head adapted for one cylinder or the cylinder head may be adapted for two or more cylinders. Usually, on larger diesel engines, the cylinder heads are individual, separate cylinder heads. The cooling channels of a cylinder head are connected to the cooling channels of the cylinder block and form part of the cooling system of the engine. The number of the valves and the position of the valves and the injector may vary between different engines.

In the shown example, inserts 15 are mounted through the fireface wall 13 such that they extend into the cooling channel 14. In the shown example, four inserts are mounted symmetrically around the injector opening 3, with one insert between two valve openings. The purpose of the inserts is to help to cool down the fireface area. This is achieved in that the inserts are made form a material having a higher thermal conductivity than the cylinder head material. A cylinder head is normally made from cast iron. The inserts are thus preferably made from aluminium or copper, which both have a high thermal conductivity. It is also possible to use an alloy comprising at least one of these materials or other material having a high thermal conductivity, such as materials comprising graphite or graphene. One advantage of using aluminium or copper is that those materials can be deformed some during insertion, which will ensure that the inserts provides a gastight fit in the fireface wall.

The inserts are mounted in openings created in the fireface after the cylinder head is cast. The openings are drilled, routed or spark wire cut through the fireface wall, preferably with a slight tapering towards the cooling channel of the cylinder head. Such a tapering will aid the mounting of the inserts. It is e.g. possible to use inserts with are slightly longer than necessary. When the inserts have been pressed into the openings with a predefined pressure, the excessive length of the inserts can be removed by grinding or routing. This will ensure that the inserts are mounted with the predefined pressure and that the surface of the inserts are flush with the fireface, which in turn will ensure that the inserts transfers as much heat as possible.

It is also possible to mount the inserts at other positions. However, the central area of the fireface around the injector opening is put under large stress during the use of the engine. One reason is that the fuel flame during combustion will have the highest temperature where the fuel is injected into the combustion chamber. Another reason is that this area is weakened by the injector opening and the valve openings. Further, cooling channels are also provided inside the cylinder head in order to cool the fireface. The cooling channels will decrease the fireface wall thickness and thus the stability of the fireface wall in order to improve the cooling of the cylinder head. The mechanical stability must thus be compromised with regards to the cooling of the cylinder head. By using inserts as described here, the risk of cracks forming in the fireface is reduced.

By lowering the temperature of the fireface, and also by equalizing the temperature gradient of the fireface, the high cycle fatigue strength is improved, which will limit the crack initiation in the fireface. Further, a lower temperature will also improve the low cycle fatigue strength which will prevent cracks from expanding through the material. The shape of the openings is preferably round and slightly tapered, as holes with this shape is easy and cost-effective to produce, and also the inserts are easy to produce in a corresponding shape. It is however also possible to use openings and inserts in other shapes. An alternative insert shape is shown in Fig. 4. An oval shape is fairly easy to produce, and it would also be possible to use an arched shape. When using a material such as aluminium or copper for the inserts, the insert will deform some when it is pressed into the opening, such that there will be a close fit between the opening and the insert that is gas tight. One advantage of mounting the inserts in the cylinder head after the cylinder head is cast is that the inserts will not displace or deform when the cylinder head is cast. In this way, insert having a melting temperature lower than the material of the cylinder head can be used. The precision of the position for the inserts is also improved compared with inserts that is cast in the material, which allows inserts to be used on positions that is otherwise not possible to achieve. Another advantage is that no material will deposit on the part of the insert that extends into the cooling channel during the casting. Such a material could be either material from the cylinder head or different oxides formed by the heat. A good cooling effect by the inserts is thus ensured.

In a development of the invention, the inner end of an insert is provided with one or more transversal flow channels. Such a flow channel is perpendicular to the centre axis of the insert. The flow channel or flow channels are provided in the part of the insets that extends into the cooling channel. A flow channel will enlarge the contact surface between the insert and the cooling fluid of the cooling channel. A flow channel will further reduce the pressure drop over the insert in the cooling channel. In this way, the insert can extend relatively much into the cooling channel without limiting the flow in the cooling channel. This will improve the cooling of the fireface further. The invention is not to be regarded as being limited to the embodiments described above, a number of additional variants and modifications being possible within the scope of the subsequent patent claims.

REFERENCE SIGNS

1 : Cylinder head

2: Injector

3: Injector opening 4: Inlet valve

5: Inlet valve

6: Exhaust valve

7: Exhaust valve

8: Inlet valve opening 9: Inlet valve opening

10: Exhaust valve opening

1 1 : Exhaust valve opening

12: Fireface

13: Fireface wall

14: Cooling channel

15: Insert

Claims

1. Cylinder head (1) for a combustion engine, comprising at least one inlet valve opening (8, 9), at least one exhaust valve opening (10, 11), at least one injector opening (3) and at least one cooling channel (14), characterized in that the cylinder head (1) further comprises at least one insert (15) in the fireface wall (13) extending from the fireface (12) of the cylinder head into the cooling channel ( 4) of the cylinder head, where the insert (15) is made of a material having a higher thermal conductivity than the cylinder head material.

2. Cylinder head according to claim 1, characterized in that the insert material is aluminium, copper or an alloy of at least one of these materials.

3. Cylinder head according to any of the preceding claims, characterized in that the insert (15) has a circular shape.

4. Cylinder head according to any of claims 1 to 3, characterized in that the insert (15) has an oval shape.

5. Cylinder head according to any of the preceding claims, characterized in that the insert (15) is tapered towards the cooling channel (14).

6. Cylinder head according to any of the preceding claims, characterized in that the insert (15) is positioned between an inlet valve opening (8, 9) and an exhaust valve opening (10, 11).

7. Cylinder head according to claim 5, characterized in that the insert (15) is positioned in the close vicinity of the injection opening (3).

8. Cylinder head according to any of the preceding claims, characterized in that the insert (15) is mounted into the fireface wall (13) after the cylinder head is cast.

9. Cylinder head according to any of the preceding claims, characterized in that the inner end of an insert (15) is provided with at least one flow channel that is perpendicular to the centre axis of the insert.

10. Engine comprising at least one cylinder head according to any of the preceding claims.

11. Method for increasing the cooling of the fireface of a cylinder head, comprising the steps of:

- producing at least one hole through the fireface wall from the fireface of the cylinder head to a cooling channel inside the cylinder head, - inserting an insert into the hole such that the insert extends into the cooling channel, where the material of the insert has a higher thermal conductivity than the cylinder head material.

12. Method according to claim 11, where the hole is produced by drilling, routing or spark eroding.

13. Method according to claim 11 or 12, where the hole is tapered towards the cooling channel.