GB2065770A

GB2065770A - Valve Seat Insert for an Internal Combustion Engine

Info

Publication number: GB2065770A
Application number: GB8040333A
Authority: GB
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1979-12-18
Filing date: 1980-12-17
Publication date: 1981-07-01
Also published as: FR2488652B1; DE2950964A1; IT8026590A0; FR2488652A1; JPS5698514A; DD155539A1; IN153951B; HU183271B; SE8008896L; SE441851B; GB2065770B; CH652800A5; IT1134690B

Abstract

The valve seat insert (3) has a substantially rectangular cross section and a height (h) in mm less than or equal to the quotient of 55 and the mean temperature gradient (T1-T2)/a, in use, measured in K/mm at the combustion chamber side of the cylinder head (2). The temperature gradient is the difference between the temperature (T1) at the centre (6) of a bridge portion of the cylinder head between two inserts (3, 4) and the temperature (T2) near the cylinder bore (1) divided by the distance (a) in mm between the points (6, 7) at which the temperatures are measured. <IMAGE>

Description

SPECIFICATION Valve Seat Insert for an Internal Combustion Engine This invention relates to a valve seat insert for an internal combustion engine, particularly but not exclusively for an exhaust valve of an aircompression, direct-injection internal combustion engine in which the cylinder head is subjected to high thermal loading, and the cylinder bore is between 80 and 1 50 mm.

Valve seat inserts for internal combustion engines are today mostly made of special cast iron with chromium and molybdenum additions.

Generally, these inserts sufficiently withstand the stresses arising. However, in the case of aircompression, direct-injection internal combustion engines, it may happen, depending on the mixture formation and/or combustion system used and the construction of the engine, that the combustion-chamber side of the bridge portion between the inlet valve and the exhaust valve in the cylinder head attains temperatures of 4000C and more. This is mainly the case where a high air swirl intensity exists in the combustion chamber and small combustion chamber openings are provided.

At such temperatures, cracks are liable to occur in the exhaust-valve seat insert, and these may lead to engine defects and failure of the engine. The cracks tend to form in the area of the valve bridge, because it is there where the highest temperature prevails, and the cylinder head underside is subject to maximum bending due to the large temperature gradients. The bending stresses caused in the valve seat insert by thermal bending in conjunction with the mechanical stresses will lead to the crack formation described.

An object of the present invention is to provide a valve seat insert without resorting to the use of expensive materials and without complicating the manufacture or installation of the valve seat inserts.

The invention provides a valve seat insert for an internal combustion engine having a substantially rectangular cross-section and a height in mm less than or equal to the quotient of 55 and, in use, the mean temperature gradient measured in K/mm at the combustion chamber side of the cylinder head.

Thus, in use the tensile stresses caused by the bending of the valve seat insert are reduced by decreasing the height of the seat insert or by limiting it to an amount where the tensile stresses can still be absorbed by the material.

Preferably, the mean temperature gradient in K/mm is determined from the difference between the combustion chamber side temperatures at the cylinder head substantially at the centre of the bridge between adjacent inserts and the temperature near the cylinder bore, the temperature gradient being derived from this temperature difference divided by the distance in mm between the points at which the temperatures are measured.

In this manner, the actual mean temperature gradient is obtained which is the key parameter for the considerations underlying the invention.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows the arrangement of the valve seat inserts in a cylinder head viewed from the combustion chamber, Figure 2 is a section taken along the line Il-Il in Figure 1, Figure 3 is a section taken along the line Ill-Ill in Figure 1 in which the thermal deformation of the cylinder head underside is shown schematically.

In Figures 1-3 an internal combustion engine is provided with a cylinder 1 and a cylinder head 2 made predominantly of grey cast iron.

The cylinder 1 has a diameter D and its centre is formed by the intersection of two axes x, y.

Inside this diameter D, the cylinder head 2 is fitted with a smaller valve seat insert 3 for an exhaust valve (not shown), and a larger valve seat insert 4 for an inlet valve (not shown).

As can be seen from Figure 1, the centres of the valve seat inserts 3,4 lie on an axis Wwhich is parallel with, but is laterally offset by a distance e from, the axis x. If, during operation, the engine is subjected to thermal stresses so that temperature of 4000C and more occur at the combustionchamber-side surface of the underside of the cylinder head 2 in the area of the valve bridge, which is the portion between the two valve seat inserts 3, 4, the underside of the cylinder head 2 will bend as shown in Figure 3 in the direction of the axis z towards the combustion chamber.

Cracking is likely to occur in the area 5 of the valve seat insert 3 for the exhaust valve. In order to prevent this, the temperature T, at the combustion-chamber-side surface on the underside of the cylinder head 2 at point 6 is measured, i.e. substantially at the centre of the bridge, and the temperature T2 at point 7 near the wall of the cylinder 1 is measured. T2 is subtracted from T1 and the result is divided by the distance a between the two points 6 and 7. In this manner, the mean temperature gradient T grad in K/mm is obtained, i.e. T grad=(T-T2)/a.

If then crack formation is to be avoided in the valve seat inserts 3, 4, their height or thickness h in mm must be smaller than or, at the most, equal to 55/grad T.

It should be mentioned that the distance a can also be determined by deducting from half the cylinder diameter D/2 the distance e(a=D/2-e, in mm).

Claims

1. A valve seat insert for an internal combustion engine having a substantially rectangular cross section and a height in mm less than or equal to the quotient of 55 and, in use, the mean temperature gradient measured in K/mm at

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Valve Seat Insert for an Internal Combustion Engine This invention relates to a valve seat insert for an internal combustion engine, particularly but not exclusively for an exhaust valve of an aircompression, direct-injection internal combustion engine in which the cylinder head is subjected to high thermal loading, and the cylinder bore is between 80 and 1 50 mm. Valve seat inserts for internal combustion engines are today mostly made of special cast iron with chromium and molybdenum additions. Generally, these inserts sufficiently withstand the stresses arising. However, in the case of aircompression, direct-injection internal combustion engines, it may happen, depending on the mixture formation and/or combustion system used and the construction of the engine, that the combustion-chamber side of the bridge portion between the inlet valve and the exhaust valve in the cylinder head attains temperatures of 4000C and more. This is mainly the case where a high air swirl intensity exists in the combustion chamber and small combustion chamber openings are provided. At such temperatures, cracks are liable to occur in the exhaust-valve seat insert, and these may lead to engine defects and failure of the engine. The cracks tend to form in the area of the valve bridge, because it is there where the highest temperature prevails, and the cylinder head underside is subject to maximum bending due to the large temperature gradients. The bending stresses caused in the valve seat insert by thermal bending in conjunction with the mechanical stresses will lead to the crack formation described. An object of the present invention is to provide a valve seat insert without resorting to the use of expensive materials and without complicating the manufacture or installation of the valve seat inserts. The invention provides a valve seat insert for an internal combustion engine having a substantially rectangular cross-section and a height in mm less than or equal to the quotient of 55 and, in use, the mean temperature gradient measured in K/mm at the combustion chamber side of the cylinder head. Thus, in use the tensile stresses caused by the bending of the valve seat insert are reduced by decreasing the height of the seat insert or by limiting it to an amount where the tensile stresses can still be absorbed by the material. Preferably, the mean temperature gradient in K/mm is determined from the difference between the combustion chamber side temperatures at the cylinder head substantially at the centre of the bridge between adjacent inserts and the temperature near the cylinder bore, the temperature gradient being derived from this temperature difference divided by the distance in mm between the points at which the temperatures are measured. In this manner, the actual mean temperature gradient is obtained which is the key parameter for the considerations underlying the invention. An embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows the arrangement of the valve seat inserts in a cylinder head viewed from the combustion chamber, Figure 2 is a section taken along the line Il-Il in Figure 1, Figure 3 is a section taken along the line Ill-Ill in Figure 1 in which the thermal deformation of the cylinder head underside is shown schematically. In Figures 1-3 an internal combustion engine is provided with a cylinder 1 and a cylinder head 2 made predominantly of grey cast iron. The cylinder 1 has a diameter D and its centre is formed by the intersection of two axes x, y. Inside this diameter D, the cylinder head 2 is fitted with a smaller valve seat insert 3 for an exhaust valve (not shown), and a larger valve seat insert 4 for an inlet valve (not shown). As can be seen from Figure 1, the centres of the valve seat inserts 3,4 lie on an axis Wwhich is parallel with, but is laterally offset by a distance e from, the axis x. If, during operation, the engine is subjected to thermal stresses so that temperature of 4000C and more occur at the combustionchamber-side surface of the underside of the cylinder head 2 in the area of the valve bridge, which is the portion between the two valve seat inserts 3, 4, the underside of the cylinder head 2 will bend as shown in Figure 3 in the direction of the axis z towards the combustion chamber. Cracking is likely to occur in the area 5 of the valve seat insert 3 for the exhaust valve. In order to prevent this, the temperature T, at the combustion-chamber-side surface on the underside of the cylinder head 2 at point 6 is measured, i.e. substantially at the centre of the bridge, and the temperature T2 at point 7 near the wall of the cylinder 1 is measured. T2 is subtracted from T1 and the result is divided by the distance a between the two points 6 and 7. In this manner, the mean temperature gradient T grad in K/mm is obtained, i.e. T grad=(T-T2)/a. If then crack formation is to be avoided in the valve seat inserts 3, 4, their height or thickness h in mm must be smaller than or, at the most, equal to 55/grad T. It should be mentioned that the distance a can also be determined by deducting from half the cylinder diameter D/2 the distance e(a=D/2-e, in mm). Claims

1. A valve seat insert for an internal combustion engine having a substantially rectangular cross section and a height in mm less than or equal to the quotient of 55 and, in use, the mean temperature gradient measured in K/mm at the combustion chamber side of the cylinder head.

2. A valve seat insert as claimed in Claim 1, wherein the mean temperature gradient in K/mm is determined from the difference between the combustion chamber side temperatures at the cylinder head substantially at the centre of the bridge between adjacent inserts and the temperature near the cylinder bore, the temperature gradient being derived from this temperature difference divided by the distance in mm between the points at which the temperatures are measured.

3. A valve seat insert substantially as herein described with reference to the accompanying drawing.

4. An internal combustion engine having a valve seat with an insert as claimed in any one of the preceding claims.