GB2193529A - Internal combustion engines - Google Patents

Abstract

A monoblock engine, i.e. one in which cylinder block and cylinder head are integrally formed, comprises a preformed unitary skeleton 10 of a hard metal cast in situ within a less dense matrix 12 forming the remainder of the engine block, the skeleton including at least cylinder liners 14 and valve seats 16 for the engine cylinders in the block. Galleries 30, 32 and 42 are for engine coolant and gallery 31 is for the circulation of exhaust gases via valves, which are only open when the engine is cold, in order to achieve rapid warming of the engine. <IMAGE>

Description

SPECIFICATION Internal combustion engines The present invention relates to the manufacture of internal combustion engines and is particularly concerned with the construction of monoblock engines in which the cylinder head is formed integrally with at least the cylinder block.

In order to reduce the weight of an engine, is is known to form the block and the cylinder head from a light material such as aluminium or an aluminium alloy. It is also generally regarded that the aluminium has better heat transfer properties than the more conventionally used cast iron. More recently it has also been proposed to use plastics materials.

Such light materials, however, are not well suited to withstand the stresses and the wear to which they are subjected in certain parts of the engine, notably the cylinder walls and the valve seats. For this reason, engine manufacturers have resorted to a composite construction in which iron is used for the cylinder walls, the valve seats and similar parts, the iron parts taking the form of liners and inserts. Valve inserts and cylinder liners are usually placed in the cylinder head and the engine block after the casting of these parts from a light material. In the case of an aluminium block, this is carried out by heating the block or cylinder head and/or cooling the iron insert or liner and shrink fitting the parts in position.

Such assembly is costly both in terms of time and energy. In the case of the cylinder liners it has also been proposed previously that they be cast in situ, but the construction of the cylinder block mould in this case was complex as the cylinder liners had to be held securely in position in the mould during the casting of the lighter metal.

In the case of a monoblock engine, it is difficult to assemble valve seats after casting of the engine block. since access must be gained to the seats from the underside of the cylinders, that it to say from the crank case end.

The manufacture of a monoblock engine as a composite structure of light and strong metals therefore presents many difficulties and the invention seeks to provide a method of construction of an engine in which such difficulties are at least partly mitigated.

According to the present invention, there is provided a method of constructing a monoblock internal combustion engine in which the engine block is formed of a composite structure having a hard metal at least along the walls of the cylinders and at the valve seats, the parts of the block not formed of hard metal being formed pf a material less dense than the hard metal, which method comprises casting a unitary skeleton including all the parts of the engine block formed of the hard metal, placing the skeleton in a mould and casting and the less dense material while the skeleton is in situ within the mould.

According to a second aspect of the invention, there is provided a monoblock engine comprising a preformed unitary skeleton of a hard metal cast in situ within a lighter matrix forming the remainder of the engine block, the skeleton including at least cylinder liners and valve seats for the engine cylinders in the block.

The invention obviates the need for expensive tooling to maintain proper alignment of the components cast in situ as they form part of a rigid skeleton and are held in their correct position by virtue of being preformed integrally with one another.

Because of the skeletal construction proposed in the invention, it possible to include a larger number of components of the hard metal without making the assembly more complex and costly. Thus according to preferred features of the invention, the skeleton may further include one or more of the following components, namely valve guides, pillar blocks for the crank shaft and overhead cam shaft, exhaust and inlet ports, threaded inserts for the spark plugs and flame plates at the top of the combustion chambers. In this way, the invention enables each component of the engine to be made from the material which is best suited to its function and no compromise need be made to gain the advantages that stem from the use of less dense or light materials such as aluminium alloys in the engine block.

It is possible to include galleries in the hard metal casting which extend along the length of the engine block in the region of the top of the combustion chambers. It is advantageous to form one such gallery for circulation of a coolant so as to cool the valves, the valve guides and the top end of the engine.

During start up, it is desirable to ensure that the engine should reach its optimum operating temperature with a minimum of delay and with this aim in mind it is further preferred to provide a gallery in thermal contact with the inlet ports and communicating by way of selectively operable valves with the exhaust ports.

The latter valves are opened under low temperature to permit the exhaust gases to flow through the gallery to heat the intake air mixture. During starting, before the temperature of the liquid coolant has risen sufficiently to operate the thermostat, the exhaust gases are diverted to flow through the latter gallery which heats the cylinder head and the inlet ports to accelerate the warm up of the engine. Under normal running temperatures, the valves leading from the exhaust ports to this gallery are closed.

It is often necessary in order to comply with packaging problems dictated by the size and shape of the engine compartment to re duce the length of an engine and minimise the distance between the cylinders. In non-monob lock engines, in which the cylinder head is removable, one can allow the crank shaft main bearing blocks to intrude upon the cylinder bores since the pistons can be introduced into the cylinder bores from above prior to as sembly of the cylinder head. In the case of a monoblock engine, this of course is not pos sible and bringing the cylinders closer together reduces the permissible width of the crank shaft main bearing blocks.

A conventional friction bearing, that is to say a bearing such- as a white metal bearing in which the surfaces slide over one another, re lies on a film of lubricant to separate the surfaces. The lubricant is fed to a groove which extends circumferentially around the bearing shell and distributes the lubricant to the entire circumference of the bearing. The lubricant flows axially in both directions away from the groove and if the width of the bearing on either side of the groove is too small, then the lubricant escapes too readily and the bear ing surfaces are allowed to contact one another, with damaging consequences.

Hitherto, it has always been regarded as es sential to include an oil groove but in the presence of such a groove the effective width of the bearing is only equal to the widths of the two lands on each side of the central oil groove. It is therefore preferred according to a further feature of the invention to employ a narrower bearing without a central circumfer ential oil groove and in which the oil is fed to the bearing surfaces by way of a bore formed in with the crank shaft. The fact that the oil bore is formed in the crank shaft rather than in the stationary part of the bearing has cer tain advantageous effects.First, the oil is naturally distributed over the surface of the bearing by the rotation of the crank shaft without the need for an oil groove thereby increasing the effective width of the bearing and enabling a narrower bearing to withstand a greater load. A second advantage is that the centrifugal force acting on the oil in the crank shaft increases the oil pressure at the bearing without the use of a high pressure oil pump, thus reducing the oil pump losses of the en gine.

The invention will now be described further, by way of example, with reference to the ac companying drawing, which is a section through a monoblock engine constructed in accordance with the invention.

The engine block illustrated in the drawing is a composite block comprising a preformed cast iron skeleton 10 cast within an aluminium matrix 12. The skeleton 10 is a unitary structure, that is to say it is formed in one piece, and includes cylinder liners 14, valve seats 16, valve guides 18, and certain other compo nents to be described below. The drawing only shows one cylinder but a single casting is used for all the cylinders in a block.

The skeleton also includes a flame plate 17 and a socket for the spark plug which is not arranged in the same plane as the section in the drawing and is not therefore shown. The inlet and exhaust ports 22 and 24 also form part of the skeleton 10 and though the parts of the ports made of cast iron are shown as extending to meet the induction manifold, the inlet ports may alternatively be partly formed in the aluminium matrix 12, if desired. The illustrated construction is advantageous in that it avoids any discontinuity or step between the cast iron and aluminium parts of the intake ports.

Three galleries or fluid passages 30, 31 and 32 are formed as part of the skeleton and extend along the length of the engine block, into the plane of drawing. The lower gallery 30 and the upper gallery 32 are for circulation of the engine coolant and serve the cool the cylinder head, the ports and the valve guides 18. The remaining gallery 31 is for circulation of exhaust gases and is connected to the exhaust ports by valves which are only open when the engine is cold. The purpose of the gallery 31 is to achieve more rapid warm up by making use of the heat in the exhaust gases.

At the lower end of the engine, the skeleton includes pillar blocks 40 which are cast as part of the skeleton. The pillar blocks 40 are relatively narrow for the engine capacity, and do not intrude on the cylinder bores as this would prevent insertion of the pistons from below into the cylinders. No oil passages are formed in the pillar blocks and instead the crank shaft (not shown) is formed with oil bores which open onto the inner surface of the bearing shells retained within the pillar blocks 40. The bearing shells have no oil groove and their entire surface therefore contributes to the load bearing. It is this construction which permits the use of narrower main bearing shells to allow the cylinders to be cast closer to one another.

The cast iron skeleton is moulded within the aluminium matrix 12 which forms in places grips the skeleton and in others is spaced from the skeleton 10 to form a water jacket 42 for the engine coolant. The coolant circulates in particular around the top of the cylinders and in the space between adjacent cylinders. The lower end 44 of the aluminium matrix 12 defines the upper half of the oil sump, while at the upper end the matrix 12 is formed with pillars (not shown) for supporting a rocker shaft and an overhead cam shaft.

It is alternatively possible to form the pillars for supporting the rocker shaft and the overhead cam shaft as part of the skeleton rather than the aluminium matrix if additional strength is required for the cam shaft bearings.

Claims (9)

1. A method of constructing a monoblock internal combustion engine in which the engine block is formed of a composite structure having a hard metal at least along the walls of the cylinders and at the valve seats, the parts of the block not formed of hard metal being formed of a material less dense than the hard metal, which method comprises casting a unitary skeleton including all the parts of the engine block formed of the hard metal, placing the skeleton in a mould and casting and the less dense material while the skeleton is in situ within the mould.

2. A monoblock engine comprising a preformed unitary skeleton of a hard metal cast in situ within a lighter matrix forming the remainder of the engine block, the skeleton including at least cylinder liners and valve seats for the engine cylinders in the block.

3. An engine as claimed in claim 2, wherein the skeleton further includes any one or more of the following components, namely valve guides, pillar blocks for the crank shaft and overhead cam shaft, exhaust and inlet ports, threaded inserts for the spark plugs and flame plates at the top of the combustion chambers.

4. An engine as claimed in claim 2 or 3, wherein at least one gallery for passage of a fluid is formed in the hard metal casting and extends along the length of the engine block in the region of the top of the combustion chambers.

5. An engine as claimed in claim 4, wherein a gallery is formed for circulation of a coolant so as to cool the valves, the valve guides and the top end of the engine.

6. An engine vas claimed in claim 4 or 5, comprising a gallery in thermal contact with the inlet ports and communicating by way of selectively operable valves with the exhaust ports.

7. An engine as claimed in any one of ciaims 2 to 6, wherein pillar blocks for the main crank shaft bearing are formed as part of the skeleton.

8. An engine as claimed in claim 7 wherein the pillar blocks do not substantially overlap the bores and haven oil supply bores, and wherein the bearing sheil of the crank shaft main bearing have no circumferential oil groove and re lubricated by means of an oil passage formed within the crank shaft.

9. An engine constructed substantailly as herein described with reference to and as illlustrated in the accompanying drawing.