GB2172338A - I.C. engine cylinder head exhaust passage inserts - Google Patents

Abstract

Each insert is constituted by a bimetallic body comprising an inner wall (24) of metal with a high thermal resistance and an outer wall (26) joined to the inner wall by spot welds and defining therewith an annular chamber (27). Each insert (22) is incorporated in the cast during casting of the light alloy head (10). <IMAGE>

Description

SPECIFICATION Cylinder head for internal combustion engines The present invention relates to a cylinder head for an internal combustion engine having exhaust ducts each of which contains a tubular insert for insulating the wall of the duct thermally from the exhaust gases.

Such tubular inserts are inserted in exhaust ducts so as to reduce the quantity of heat transferred from the exhaust gases to the walls of the exhaust ducts, both to avoid excessive heating of the engine coolant by conduction through the exhaust-duct walls and to reduce the emission of pollutants into the atmosphere in the exhaust gases produced by the engine by keeping the exhaust gases at a high temperature downstream of the exhaust valves.

In the prior art, various configurations have been proposed for the cylinder heads of internal combustion engines in orderto improve the thermal insulation of the exhaust gases within the tubular inserts.

The most effective solutions from the point of view of thermal insulation provide for the formation of wide, annular interspaces between the inserts and the inner walls of the exhaust ducts, these possibly being sealed and filled with air or with thermallyinsulating solid materials.

These solutions are extremely expensive and difficult to put into practice.

The object of the present invention is to avoid these disadvantages and to provide a cylinder head of the type defined at the beginning, the tubular inserts whereof are relatively cheap and simple to make, are easy to fit and at the same time, are extremely effective from the point of view of thermal insulation of the exhaust gases.

According to the invention this object is achieved by virtue of the fact that each tubular insert is constituted by a bimetallic body comprising an inner wall of metal with a high thermal resistance and an outer wall joined to the inner wall and defining therewith an annular, intermediate chamber, the bimetallic insert being incorporated in the cast during casting of the head.

The inner, high-thermal-resistance wall is preferably made from a special Inconel (RTM) steel while ordinary steel may be used for the outer wall.

The incorporation in the cast during casting of the head may be effected either by incorporation in the moulding core by means of binders or by positioning in the shell by means of metal connectors.

The invention will now be described in detail with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure 1 is a schematic, longitudinal-sectional view of part of an internal-combustion-engine cylin der head according to the invention, and Figure 2 is a cross-sectional view taken on the line ll-ll of Figure 1.

With reference to the drawings, part of a cylinder head of a multi-cylinder, internal-combustion engine for motor vehicles is indicated 10 and is formed in a single block by casting from light alloy.

The head 10 has a plurality of exhaust ducts within it only one of which is indicated 12. The exhaust duct 12 communicates at one end with the combustion chamber 16 of the cylinder and at its opposite end, through an exhaust aperture 14, with an exhaust manifold ndt illustrated.

The inner end of the exhaust duct 12 has an added valve seat 18 disposed coaxially with a passage 20 formed during casting of the head 10 for guiding the respective exhaust valve.

Within each exhaust duct 12 is a tubular, bimetallic insert 22 having a profile similar to that of the duct 12.

The tubular insert 22 is constituted by an inner wall 24 of a metal with a high thermal resistance, normally a special Inconel (RTM) steel alloy 601, and an outer wall 26 usually of ordinary steel.

The two walls 24 and 26 are spaced from each other so as to define an annular interspace 27 and are interconnected, normally by spot welds 28.

This conformation gives a very high thermallyinsulating capacity towards the exhaust gases within the duct 12 during running of the engine, with a noticeable reduction both in the emission of pollutants in these gases and in the quantity of heat transferred from the gases to the head 10.

According to the invention, the tubular inserts 22 are actually incorporated in the cast during casting of the head 10. This may be achieved either by incorporation in the moulding core or by positioning in the shell by means of metal connectors.

The incorporation of the inserts 22 in the cast for the head 10 obviously gives the best guarantee of hermetic sealing.

Naturally the scope of the present invention extends to models which achieve equal utility by using the same innovative concept.

1. Alight-alloy cylinder head for an internal combustion engine having exhaust ducts each of which contains a tubular insert for insulating the duct wall thermally from the exhaust gases, each tubular insert being constituted by a bimetallic body comprising an inner wall of a metal with a high thermal resistance and an outer wall joined to the inner wall and defining therewith an annular chamber, the bimetallic insert being incorporated in the cast during casting of the head.

2. A cylinder head according to Claim 1, in which the inner wall of each bimetallic insert is of a special Inconel (RTM) steel.

3. A cylinder head according to Claim 1 or Claim 2, in which the outer wall of each bimetallic insert is of ordinary steel.

4. A cylinder head according to any one of the preceding claims, in which the outer wall and the inner wall of each bimetallic insert are interconnected by spot welds.

5. A cylinder head substantially as herein described with reference to, and as shown in, the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Cylinder head for internal combustion engines The present invention relates to a cylinder head for an internal combustion engine having exhaust ducts each of which contains a tubular insert for insulating the wall of the duct thermally from the exhaust gases. Such tubular inserts are inserted in exhaust ducts so as to reduce the quantity of heat transferred from the exhaust gases to the walls of the exhaust ducts, both to avoid excessive heating of the engine coolant by conduction through the exhaust-duct walls and to reduce the emission of pollutants into the atmosphere in the exhaust gases produced by the engine by keeping the exhaust gases at a high temperature downstream of the exhaust valves. In the prior art, various configurations have been proposed for the cylinder heads of internal combustion engines in orderto improve the thermal insulation of the exhaust gases within the tubular inserts. The most effective solutions from the point of view of thermal insulation provide for the formation of wide, annular interspaces between the inserts and the inner walls of the exhaust ducts, these possibly being sealed and filled with air or with thermallyinsulating solid materials. These solutions are extremely expensive and difficult to put into practice. The object of the present invention is to avoid these disadvantages and to provide a cylinder head of the type defined at the beginning, the tubular inserts whereof are relatively cheap and simple to make, are easy to fit and at the same time, are extremely effective from the point of view of thermal insulation of the exhaust gases. According to the invention this object is achieved by virtue of the fact that each tubular insert is constituted by a bimetallic body comprising an inner wall of metal with a high thermal resistance and an outer wall joined to the inner wall and defining therewith an annular, intermediate chamber, the bimetallic insert being incorporated in the cast during casting of the head. The inner, high-thermal-resistance wall is preferably made from a special Inconel (RTM) steel while ordinary steel may be used for the outer wall. The incorporation in the cast during casting of the head may be effected either by incorporation in the moulding core by means of binders or by positioning in the shell by means of metal connectors. The invention will now be described in detail with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure 1 is a schematic, longitudinal-sectional view of part of an internal-combustion-engine cylin der head according to the invention, and Figure 2 is a cross-sectional view taken on the line ll-ll of Figure 1. With reference to the drawings, part of a cylinder head of a multi-cylinder, internal-combustion engine for motor vehicles is indicated 10 and is formed in a single block by casting from light alloy. The head 10 has a plurality of exhaust ducts within it only one of which is indicated 12. The exhaust duct 12 communicates at one end with the combustion chamber 16 of the cylinder and at its opposite end, through an exhaust aperture 14, with an exhaust manifold ndt illustrated. The inner end of the exhaust duct 12 has an added valve seat 18 disposed coaxially with a passage 20 formed during casting of the head 10 for guiding the respective exhaust valve. Within each exhaust duct 12 is a tubular, bimetallic insert 22 having a profile similar to that of the duct 12. The tubular insert 22 is constituted by an inner wall 24 of a metal with a high thermal resistance, normally a special Inconel (RTM) steel alloy 601, and an outer wall 26 usually of ordinary steel. The two walls 24 and 26 are spaced from each other so as to define an annular interspace 27 and are interconnected, normally by spot welds 28. This conformation gives a very high thermallyinsulating capacity towards the exhaust gases within the duct 12 during running of the engine, with a noticeable reduction both in the emission of pollutants in these gases and in the quantity of heat transferred from the gases to the head 10. According to the invention, the tubular inserts 22 are actually incorporated in the cast during casting of the head 10. This may be achieved either by incorporation in the moulding core or by positioning in the shell by means of metal connectors. The incorporation of the inserts 22 in the cast for the head 10 obviously gives the best guarantee of hermetic sealing. Naturally the scope of the present invention extends to models which achieve equal utility by using the same innovative concept. CLAIMS

1. Alight-alloy cylinder head for an internal combustion engine having exhaust ducts each of which contains a tubular insert for insulating the duct wall thermally from the exhaust gases, each tubular insert being constituted by a bimetallic body comprising an inner wall of a metal with a high thermal resistance and an outer wall joined to the inner wall and defining therewith an annular chamber, the bimetallic insert being incorporated in the cast during casting of the head.

2. A cylinder head according to Claim 1, in which the inner wall of each bimetallic insert is of a special Inconel (RTM) steel.

3. A cylinder head according to Claim 1 or Claim 2, in which the outer wall of each bimetallic insert is of ordinary steel.

4. A cylinder head according to any one of the preceding claims, in which the outer wall and the inner wall of each bimetallic insert are interconnected by spot welds.

5. A cylinder head substantially as herein described with reference to, and as shown in, the accompanying drawings.