An internal combustion engine

Abstract

 An internal combustion engine has a plastics block with metal cylinder liners and a metal cylinder head. A bed plate holds the crankshaft bearing caps against the bottom of the block. Through bolts tie all these components together. An oil pan is fitted below the bed plate.

Description

[0001] This invention relates to internal combustion engines and in particular to an internal combustion engine in which at least part of the engine structure is made of a plastics material. Conventionally internal combustion engines are made from cast metal, either iron or aluminium. There would be advantages in making at least some of the structural engine parts out of plastics materials, but there are a number of technical problems which have up to now prevented the development of a satisfactory plastics engine structure.

[0002] According to the present invention, there is provided an internal combustion engine having a metal cylinder head, a block and a bed plate, wherein the bed plate serves to support crankshaft bearings against the block, the block is made from a plastics material with metal cylinder liners and the engine is secured together by bolts extending between the cylinder head and the bed plate and through bores in the block.

[0003] The joint between the block and the cylinder head has to perform three sealing functions. Firstly it must seal provide a gas seal for the combustion chamber which is formed partly in a cylinder in the block and partly in a combustion chamber in the head and which is at a relatively high pressure. Secondly it must provide a seal for cooling water which flows between the block and the head and thirdly it must provide a seal for lubricating oil which also travels between the block and the head.

[0004] The first of these (combustion gases) is at a very high pressure (for example 1000 psi). The second and third (water and oil) are at relatively low pressures.

[0005] Conventional engine technology with a metal block and a metal cylinder head with a gasket in between has provided the same clamping force to seal all of these systems. If the clamping force is adequate to seal the high pressure gases in the combustion chambers, then it must be unnecessarily high relative to the oil and water systems in the engine.

[0006] In the present invention, a metal cylinder liner is held tightly against the metal cylinder head (with an appropriate gasket between) to seal the gases in the combustion chamber. In the case of the oil and water system however, sufficient sealing pressure can be generated between a plastic surface of the block and the metal cylinder head (with an appropriate gasket between).

[0007] If the metal cylinder liners have an external annular rib, the rib can be seated against a shoulder formed as part of the plastics engine block. In this way, the engine block can be produced as a moulded plastics item which does not require any machining subsequent to moulding. The cylinder liners will be wet cylinder liners.

[0008] Since the cast plastics materials have less torsional stiffness than metals, it is necessary to increase the stiffness at the bottom end of the block, where the crankshaft is supported. This can be done be integrating all the crankshaft caps into a common bed plate structure which may be made either of metal or of plastics.

[0009] The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic section through an engine in accordance with the invention;

Figure 2 is a section through a cylinder of the engine of Figure 1, which the cylinder head removed; and

Figure 3 is a plan view of a bed plate for use in the engine.

[0010] The engine shown in Figure 1 is made up of a cylinder head 10, an engine block 12, a bed plate 14 and an oil pan 16. The cylinder head 10 is of metal and includes a socket 18 for receiving a camshaft in the conventional way to operate the engine valves.

[0011] The block 12 is of plastics, suitably a fibre-reinforced plastics material and contains the engine cylinders. One half 20 of a crankshaft bearing is accommodated in the block 12, whilst the other half 22 of the bearing is accommodated in the bed 14. The oil pan 16 serves to enclose a space within the engine for lubricating oil.

[0012] The head 10, block 12 and bed plate 14 are all held together by bolts 24 which pass through bores in all the components and are tightened by means of nuts 26. In Figure 1, the crankshaft is indicated in section at 28.

[0013] In the internal view of the block 12 which is shown in Figure 2, a wet cylinder liner 30 has an outer annular rib 32 which is supported on a shoulder 34 which is part of the block moulding 12. It will be appreciated that the liner 30 is of metal, and will have a machined internal surface, and the shoulder 34 on which the liner rests will be of plastics.

[0014] Before the cylinder head is put into place, the cylinder liner 30 will project slightly above the surrounding surface of the plastics block 12, so that when the engine is fully clamped up there will be a greater clamping force between the upper edges of the liner 30 and the cylinder head than there will be between the outer faces of the block 12 and the head. This feature is shown on an exaggerated scale in Figure 2.

[0015] Figure 2 also shows a piston 36 in the cylinder liner 30 and a connecting rod 38 connecting the piston 36 to the crankshaft 28.

[0016] The bed plate 14 is shown in plan view, disassembled from the rest of the engine, in Figure 3. The plate has bearing caps 40 for each bearing of a five-bearing crankshaft. Bores 42 at each end of each cap 40 accommodate the through bolts 24 which tie the whole engine together. The caps 40 are connected up into a ladder-type structure by connecting webs 44 and outer walls 46. The presence of this connected structure at the lower end of the engine block provides additional torsional stiffness to support the crankshaft bearing loads.

[0017] The bed plate 14 may be made of metal or of plastics, depending on the required stiffness and the engine characteristics.

[0018] The plastics moulding technique used to produce the engine block 12 can be any suitable technique which will give the desired results. It is however anticipated that it may be advantageous to use a reinforced plastics material (e.g. a fibre reinforced material) and to increase the local reinforcement content at particular areas, notably on the faces 48 where the block seals against the cylinder head and on the surfaces of the shoulders 34 where the cylinder liners 30 are supported.

[0019] To attach the oil pan 16 to the rest of the engine, bolts 50 are used. These extend through bores 52 in the bed plate 14 and into a threaded insert 54 in the block. However, by alternative design, the inserts 54 may be omitted and the bolts 50 may extend right through the shoulder 56 on the block, where a nut can be attached.

Claims

1. An internal combustion engine having a metal cylinder head (10), a block (12) and a bed plate (14), characte­rised in that the bed plate (14) serves to support crankshaft bearings (2,22) against the block (12), the block (12) is made from a plastics material with metal cylinder liners (30) and the engine is secured together by bolts (24) extending between the cylinder head (10) and the bed plate (24) and through bores in the block (12).

2. An engine as claimed in Claim 1, characterised in that the metal cylinder liner is held tightly against the metal cylinder head (with an appropriate gasket between) to seal the gases in the combustion chamber, and the oil and water systems are sealed by a gasket between a plastic surface of the block and the metal cyclinder head.

3. An engine as claimed in Claim 1 or Claim 2, charac­terised in that the metal cylinder liners have an external annular rib, and the ribs are seated against a shoulder formed as part of the plastics engine block.

4. An engine as claimed in any preceding claim, characterised in that a bed plate is provided below the engine block, and all the crankshaft bearing caps are supported by the bed plate.

5. An engine as claimed in Claim 4, characterised in that the bed plate is a ladder-like structure.

6. An engine as claimed in Claim 4 or Claim 5, characte­rised in that the bed plate is of a plastics material.

7. An engine as claimed in Claim 4 or Claim 5, characte­rised in that the bed plate is of metal.

Drawing