GB2196385A

GB2196385A - Mounting I.C. engine crankshafts

Info

Publication number: GB2196385A
Application number: GB08625171A
Authority: GB
Inventors: Stephen Peer
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1986-10-21
Filing date: 1986-10-21
Publication date: 1988-04-27
Anticipated expiration: 2006-10-21
Also published as: GB8625171D0; GB2196385B

Abstract

The bearing housings 22 for the crankshaft main bearings 20 are separable from the cylinder block 30. The unitary sub-assembly 10 formed by mounting on the crankshaft 12 the pistons 14 and connecting rods 16, the big end bearings 18, and the bearing housings 22, shells and end caps 24 of the main bearings 20 is introduced into the cylinder block 30 and the main bearing housings 20 are secured to the cylinder block 30 by the bolts 26. The housings 20 may be cast with the block 30 and may be machined in situ prior fracture splitting of the housings from the block. <IMAGE>

Description

SPECIFICATION Internal combustion engine The present invention relates to the assembly of internal combustion engines and is particularly concerned with the step of assembling the crankshaft on an engine in an automated factory line.

It is conventional in the case of internal combustion engines used in automotive vehicles for the main bearings for the crankshaft to be friction bearings comprising two bearing shells arranged within pillar blocks.

Each pillar block includes a bearing housing formed integrally with the cylinder block and a bearing cap which is fitted over the bearing housing.

By virtue of this construction, assembly of the bearings of the crankshaft tends to be highly labour intensive since the assembly of the bearing shells and the tightening of the bearing caps to the correct torque must all be carried out with the crankshaft in situ. This operation cannot readily be carried out by robots on an automated assembly line because of the limitation on the access to the various parts.

With a view to mitigating the foregoing difficulties, there is provided in accordance with one aspect of the invention an internal combustion engine wherein the entire bearing housings for the crankshaft main bearings are separable from the cylinder block.

The bearing housings are preferably secured to the cylinder block by the bolts securing the bearing caps, the latter bolts passing through the bearing housings and engaging in threaded in the cylinder block.

In a second aspect of the invention, there is provided a method of assembling of an inter nal combustion engine, which comprises forming a unitary sub-assembly by mounting on the crankshaft the pistons and connecting rods, the big end bearings, and the bearing housings, shells and end caps of the main bearings, introducing the unitary sub-assembly into the cylinder block and securing the main bearing housings to the cylinder block.

It is advantageous to provide straps or other loose fixing means to hold the main bearing components in their correct relative positions during the introduction of the subassembly into the cylinder block.

The bearing housings and caps must be correctly aligned with one another when fitted to the engine and should therefore be machined in situ as in a conventional engine in which the main bearing housings are integral with the cylinder block. It is important that alignment means be provided to ensure that after assembly the bearing housings adopt their precise position during machining of the bearing surfaces.

This may be achieved by an alignment peg but as an alternative the bearing housing may initially be cast integrally with the cylinder block and later separated from it by fracture splitting after the bearing surfaces have been machined. Fracture splitting may also be used to separate the bearing caps from the bearings housings, as has been previously proposed in relation to big end bearings.

The invention will now be described further, by way of example, with reference to the accompanying drawing, which shows a perspective view of an engine during assembly.

The method of assembly of the invention is based on pre-assembling the moving parts of the engine and inserting them as a unitary sub-assembly into the cylinder block.

The sub-assembly is designated 10 in the drawing and comprises the crankshaft 12, the pistons 14 complete with piston rings, the connecting rods 16, the big end bearings 18 and the main bearings 20. The main bearings are formed of a bearing housing 22, a bearing cap 24 and bearing shells (not shown) arranged between the crankshaft and the pillar block formed by the housing 22 and the cap 24.

The bolts 26 for tightening the main bearings are also used for securing the main bearings to the cylinder block 30 and therefore in the sub-assembly the main bearings are not tightened. To prevent their falling apart, the bearing housing is formed with a wire strap 32 which engages in a groove or over a ridge in the bearing cap 24 to hold the two together temporarily during the assembly procedure.

To assemble the engine, the sub-assembly 10 is lowered and the portions are offered into the cylinder bores 40. It will be noted that because of the separation of the bearing housings from the cylinder block 30, access to the pistons from the sides of the engine to compress the piston rings is not impeded and it is possible for a robot to effect the assembly.

After the pistons have been introduced in pairs into the cylinder block 30 the crankshaft is fully driven down to seat the bearing housings 22 on the cylinder block 30 and thereafter the bolts 26 are tightened to their correct torque.

It is assumed that the axes of the main bearings are correctly aligned and this may be ensured by machining the bearing surface while mounted in situ on the cylinder block.

To ensure that the bearing housings are returned to their position during machining of the bearing surfaces, conventional alignment techniques may be adopted or the bearing housings may be separated from the bearing block by fracture splitting. In this method, the random surface of the fracture split can be aligned with great accuracy with the mating fracture and there is no risk of interchanging bearing housings as each fracture surface is unique.

It is alternatively possible for the bearing housings all to be machined identically within close tolerance and to be mounted on an accurately machined surface on the underside of the cylinder block to ensure alignment of the axes of the bearings when the crankshaft is assembled.

The separation of the bearing housings from -the cylinder block offers additional advantages to the simplification of the assembly procedure as will be discussed.

It is necessary because of packaging considerations to form the cylinders of an engine as closely as possible to one another. However, as the cylinder are brought together, less space is available between the cylinders to accommodate the main bearing. With engines having separate cylinder heads, the main bearing can be allowed to intrude on the cylinder bore as the cylinder bore can be machined from above and the piston into the cylinder bore from above. This, of course, complicates assembly assembly still further as the big end bearings must also be assembled in situ.

With monoblock engines, where the cylinder head is not separable from the cylinder block, the main bearing cannot intrude on the cylinder bore in a conventional engine as the bore could not be machined nor the piston introduced into the bore. The bearing is therefore thinned iocally which reduces its load bearing capacity. In the present invention, the bearing housing may be separated from the cylinder block and does not interfere with machining and assembly and may therefore be allowed to intrude on the cylinder bore.

If the bearing housing are formed separately from the cylinder block, it is possible for a shorter casting to be employed for the cylinder block. This reduces both the material cost and the casting costs.

In the latter case where is the bearing housing is not formed by fracture splitting, it is possible to machine the mating surface for the bearing housings and the mating surface for the sump at one and the same time. This reduces machining costs.

Claims

1. An internal combustion engine wherein the entire bearing housings for the crankshaft main bearings are separable from the cylinder block.

2. An internal combustion engine as claimed in claim 1, wherein the bearing housings are secured to the cylinder block by the bolts securing the bearing caps, the latter bolts passing through the bearing housings and engaging in threaded in the cylinder block.

3. An internal combustion engine as claimed in claim 2, wherein fixing means are provided to holding the main bearing components in assembled relation to one another prior to tightening of the bolts to the cylinder block.

4. A method of assembling an internal combustion engine, which comprises forming a unitary sub-assembly by mounting on the crankshaft the pistons and connecting rods, the big end bearings, and the bearing housings, shells and end caps of the main bearings, introducing the unitary sub-assembly into the cylinder block and securing the main bearing housings to the cylinder block.

5. A method as claimed in claim 4, wherein prior to assembly of the main bearing components on the crankshaft, the bearing housing and bearing caps are machined in situ on the cylinder block.

6. A method of assembling an internal combustion engine substantially as herein described with reference to and as illustrated in the accompanying drawing.