BACKGROUND OF THE INVENTION Diesel engines generally use detachable, coolant-jacketed cylinder liners, which by way of a flange between cylinder block and cylinder head are firmly clamped by means of cylinder head bolts in order to hold them in place in the cylinder block. A gasket is often also used between liner and cylinder head in order to provide a tighter seal for coolant, oil and combustion pressure.

Since the trend is towards greater peak pressures in the combustion chamber, in an order of magnitude exceeding 200 bar, for example, this also places greater demands on the gas seal between the liner and the cylinder head.

Possible ways of reinforcing the gas seal include, for example, increasing the number of bolts or uprating them to withstand greater loads. This is difficult to achieve, however, since the space is limited and the cylinder head is provided with valves together with inlet and exhaust ports for the charge cycle. In addition

there are ports for oil and coolant in the cylinder head.

Furthermore, the so-called cylinder liner shelf in the engine block has only limited strength. It is therefore difficult to achieve any substantial increase in the clamping force in the gas seal without increasing the interval between the engine cylinders, that is to say increasing the overall length of the engine.

One problem with the bolted connection described above, moreover, is that the clamping force, varying at different points along the radius of the liner, gives rise to deformations of the cylinder liner. The deformations in the cylinder liner also increase under increased clamping force.

SUMMARY OF THE INVENTION It is therefore an object of the invention to provide a gas seal which will withstand high combustion pressures and which at the same time keeps the problems described above within limits.

To this end the gas seal according to the invention is characterized in that the end section of the cylinder liner is provided with a surface, which in the position of use diverges axially towards the cylinder head and which is intended to interact with a corresponding surface on a sealing ring, converging in said direction, in order to form a radial seal inside the groove. This gas seal design means that large radial forces can be generated by a comparatively low clamping force on the cylinder head bolts, the radial forces being readily absorbed by the cylinder head via interacting seal surfaces between the end section of the cylinder liner and the sealing ring. The dimensioning of the bolts in the cylinder head is governed solely by the combustion pressure and by the resistance to intermittent load,

which can cause fatigue in the bolts, and by the requisite force needed to deform the sealing ring.

Advantageous examples of embodiments of the invention are set forth in the following dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail below with reference to examples of embodiments shown in the drawings attached, in which Fig. 1 shows a broken cross-section through a gas seal according to the invention, Fig. 2 is a partial enlargement of the gas seal shown in Fig. 1, and Fig. 3 shows the gas seal according to Fig. 2, being fitted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 shows a longitudinal section through a cylinder liner 12 in its position of use fitted to an engine block 10 and a cylinder head 11. The cylinder liner is of the freely suspended wet liner type, which can be used on all types of internal combustion engines. A piston (not shown) runs in the cylindrical bore 13 of the liner. The opposite side of the liner wall is cooled by a coolant jacket 14, which is defined at the top by a gas seal 15 and at the bottom by sealing rings 16, which are arranged in grooves in the engine block 10. Alternatively the rings 16 might be arranged in grooves in the cylinder liner.

The internal combustion engine may be a diesel engine, for example, operating with combustion pressures in excess of 200 bar. The gas seal according to the invention can also be applied to other types of internal combustion engines.

The gas seal 15 can be seen more clearly from Fig. 2.

The cylinder head 11 has a circular groove 17, which is designed to receive an end section 18 of the cylinder liner 12. In addition the cylinder head has a bearing surface 19, which is situated radially inside the groove 17 and is designed to interact with a corresponding bearing surface 20 on the cylinder liner 12. The liner bearing surface 20 is situated radially inside the annular end section 18 of the liner. The radially outer side of the annular end section is provided with a surface 21, which in the position of use diverges axially towards the cylinder head 11. The surface is intended to interact with a corresponding surface 22 on a sealing ring 23 converging in the same direction. The sealing ring is made from a material in which at least the surface layer has a lower yield point than the materials from which the cylinder block, the cylinder liner and the cylinder head are made. The cylinder block has a bearing surface 24, against which a foot section 25 of the sealing ring bears.

A gasket 26 made of steel, for example, is arranged on the outside of the annular gas seal. The gasket is not essential for the invention but may be advantageous in certain applications.

When fitting, see Fig. 3, the sealing ring 23 is applied to the liner before this is fitted in the cylinder block 10, by introducing it from the end opposite the end section 18. The liner is then lowered down into the engine block until the foot section of the sealing ring starts to touch against the bearing surface 24 of the cylinder block and the inclined surface of the sealing ring reaches the inclined surface 21 on the end section of the liner. The cylinder head can not be located on

the end section 18 of the cylinder liner, which has a rising bevel 18a that merges into a surface with an easy press fit, and the cylinder head bolts are used to create axial clamping force. The bearing surface 24 thereby presses the inclined surface 22 of the sealing ring against he inclined surface 21 on the end section of the liner, which means that the flexible sealing ring 23 slides somewhat along the end section and at the same time expands radially to form a radial seal inside the groove 17.

It can be seen from Fig. 3 that the sealing ring is provided with grooves 27 which are parallel to the ring plane. When sufficient pressure is applied to the ring, this will be plastically deformed. The grooves 27 allow the ring material to spread out into these cavities. In the event of even a slight relative movement between sealing ring and liner, the resulting radial force via the angular transmission in the interacting inclined surfaces becomes very great, which means that sealing occurs principally at the contract surfaces with the side walls of the groove. The plastic deformation of the sealing ring ensures a gas-tight seal under high gas pressures. In addition, a seal is also formed in the contact between the bearing surfaces 19,20, which define the liner fitting position. This contact is ensured by a certain clearance 27 between the end section 18 and the bottom of the groove 17. The gasket 26 furthermore possesses such elasticity that the seal between the bearing surfaces 19,20 is maximized.

The embodiment of the gas seal described above means that the coolant jacket 14 can extend right up to the sealing ring 23, that is to say to the level of the cylinder head. This makes the cooling of the cylinder liner more effective. The radial seal furthermore reduces the

deformation of the liner, so that the piston rings form a better seal against the cylinder liner, which is environmentally advantageous. Reduced deformation means that the consumption of engine lubricating oil is reduced, which leads, for example, to less soot in the exhaust gases.

The end section 18 of the cylinder liner governs the position of the cylinder head on the cylinder block, which eliminates internal stresses. In addition the end section 18, in conjunction with the sealing ring 23, functions as a vertical fastening for the liner in the engine block. On multi-cylinder engines it is advisable to allow a certain lateral mobility between the liner and the engine block, in order to compensate for positioning deviations during manufacture and in order to get coolant up to the cylinder head. The gas seal is appropriately dimensioned so that there is an easy press-fit between the inner edge side of the end section 18 and the interacting groove edge, and a tighter press-fit between the sealing ring and the cylinder liner, so that this does not slip down when fitting and dismantling.

Dismantling of the cylinder head and liner is facilitated in that the depth of the groove narrows conically towards the bottom thereof. The radially outer side of the groove appropriately forms a back angle with an incline of between approximately 92 and 96 degrees in relation to the bearing surface of the cylinder head. Friction- reducing means such as molybdenum sulfide or graphite grease/paste may be used when fitting, in order to reduce the friction between the contact surfaces. Alternatively the contact surfaces may be coated with any material having a low coefficient of friction, which also facilitates dismantling of the seal. When dismantling, the sealing ring is entirely released from the cylinder

head and the latter can be lifted off leaving liner sitting in the engine block. The sealing ring can be changed before reassembling.

The invention must not be regarded as being limited to the examples of embodiments described above, a number of further variants and modifications being feasible without departing from the cope of the following patent claims.