GB2306581A

GB2306581A - Plain bearing

Info

Publication number: GB2306581A
Application number: GB9522670A
Authority: GB
Inventors: Mark Peters
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1995-11-04
Filing date: 1995-11-04
Publication date: 1997-05-07
Also published as: WO1997017550A1; GB9522670D0

Abstract

A plain bearing comprises a bearing cap 110 which, together with a mating part (eg a cylinder head 112), forms a cylindrical bearing surface 114,115 for a shaft. The cap and its mating part have a dovetail form which allows the parts to be assembled by an axial sliding movement. One or both of the pairs of surfaces 132,134 may taper axially, whereby the cap jams in the correct axial position. The cap may be cast, or moulded from plastics or sintered metal.

Description

BEARING HOUSING This invention relates to a bearing housing. Bearing housings provide bearing surfaces or bearing supports for rotating shafts, in particular rotating shafts in internal combustion engines. One typical application to which the present invention may be suitable is the assembly of a bearing housing for the cam-shaft of a motor vehicle engine. The invention is not however limited to this application.

Traditionally, a bearing housing comprises two parts.

Each part has a semi-circular bearing surface, and the two parts when connected together form a circular surface.

Bearing shells can be fitted within the circular surface if required, the circular surface can directly form the bearing surface. A shaft journal rotates within the bearing surface. One of the housing parts is normally formed in a larger component, for example a cylinder head or an engine block. The other part is a bearing cap which is initially separate from the mating part, but will be attached thereto by suitable bolts or other threaded fasteners.

An example of such a traditional bearing housing assembly is shown in Figure 1 where a bearing cap 10 is fitted above a mating part 12, in the form of a cylinder head of an internal combustion engine. Figure 1 shows only the centre and one side of the bearing cap. The cap 10 has a semi-circular recess 14 and the mating part 12 also has a similar recess 15. When the cap and the mating part are assembled, the two semi-circular recesses 14,15 form a single circular recess.

A shaft 16 with a cylindrical journal region is to be carried in the bearing housing. In assembly, the shaft 16 is placed in the recess 15 of the mating part 12, and the cap 10 is then placed over it. To hold the cap in place and to complete the assembly of the bearing housing, bolts 18 are passed-through bores 19 in the cap and are screwed into threaded holes 20 in the mating part 12.

Only one bolt and its associated bore and threaded hole are shown in Figure 1. In practice, there will be two such bolts, spaced equidistantly either side of the axis of the shaft 16. When these bolts have been tightened, a bearing housing is formed.

The shaft 16 can be, for example, a camshaft for a motor vehicle engine.

A bearing cap 16 is usually manufactured by casting. The casting then requires machining on the semi-circular bearing surface 14, on the joint face 23 which will mate with the mating part 12 and on the surface 24 against which the head 26 of the bolt will abut. In addition, the bores 19 have to be drilled. On the mating part 12 which is also likely to be formed by casting, the surface the joint face 23 has to be machined, and the threaded hole 20 has to be drilled and tapped. There is therefore a significant quantity of machining to be done before the bearing housing can be assembled.

According to the present invention, there is provided a bearing housing comprising a bearing cap and a mating part, wherein the cap and the mating part are secured together by a sliding joint assembled by relative movement between the cap and mating part in a direction parallel to the bearing axis.

The sliding joint is preferably a dovetail tenon arrangement. The mating part preferably has an undercut track produced in the forming/casting/machining of the mating part, and the cap then has a correspondingly shaped tenon which slides into the undercut track to a position where the cap is securely held in place and radial movement of the cap cannot take place.

The housing preferably includes means for securing the cap and mating part against further sliding movement. These means may take the form of matching axial tapering forms on the mating part and the cap, so that these parts jam together when the desired extent of sliding movement has taken place. It may however be appropriate for manufacturing cost reasons to make one of the parts (eg the mating part) with a parallel-sided undercut track, with the other part having a tapered form which will jam in the parallel track.

The mating part and the cap of this assembly require machining on their semi-circular faces and on their faces adjacent and on either side of the semi-circular faces.

Further machining is however not required, and at least one of the dovetail faces can be 'as cast'. No holes are required for the fitting of securing bolts.

The cap can have a head with a domed contour which approximately follows the contour of the semi-circular recess, subject to sufficient material being present between the recess and the head to provide the required stiffness. As a result, the height of the head ab-v l joint face can be less than that of the prior art design which can assist in engine bay packaging.

The cap can be manufactured as a conventional metal forming or casting. Alternatively, the cap could be a plastic moulding or a powder metal sinter formed component.

The invention also extends to a method of assembling a bearing housing, wherein a bearing cap is slid axially of the bearing axis into an undercut region of a mating part, to form a bearing housing between the cap and the mating part.

A set of bearing caps can be positioned relative to the shaft to be journalled by the bearings, with the help of a jig, and the whole subassembly can then be offered up to the respective mating parts, for example on an engine block, and assembled in one operation.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a section through a bearing housing assembly in accordance with the prior art; Figure 2 is a section through a bearing housing assembly in accordance with the invention; Figure 3 is an exploded view of a housing assembly in accordance with the invention; and Figure 4 is a view, corresponding to Figure 2, but showing an alternative embodiment of the invention.

The housing shown in Figure 1 has already been described in the introductory part of this specification.

Figures 2 and 3 show an engine cylinder head 112 in which a camshaft 116 is to be mounted, for rotation. The cylinder head is formed with a semi-circular recess 115, a joint face 123 and an undercut groove or track 130 which has inwardly sloping faces 132. The track 130 cooperates with a bearing cap 110 which has side faces 134 corresponding to the sloping faces 132, a semi-circular recess 114 and a joint face 136.

Both the bearing cap 110 and the cylinder head 112 with which the cap mates (the cylinder head is also referred to as the mating part) are formed by any suitable metal or plastics forming process; die casting is particularly suitable. Before assembly, a machining operation takes place on the semi-cylindrical surfaces and on the joint faces. This machining operation is not essential. The machining on the cylinder head track 130 can be carried out by any suitable machining process, and broaching or milling are particularly suitable. However the sliding faces 132,134 are not necessarily machined.

To assemble the bearing housing, a shaft 116 is placed in the recess 115 and the cap 110 is lined up with one end of the track 130 and moved in a direction parallel to the coincident shaft and bearing axes to take up the position shown in Figure 2 where the two semi-circular recesses 114,115 form a cylindrical bearing surface.

In addition to the angle of inclination of the surfaces 132,134 to the joint faces 123,136, the dovetail joint will have a taper in the axial direction which will limit axial movement of the cap along the track 130. This taper (which can be that provided by the diecaster's draft angle) may appear both on the walls 132 of the track and on the walls 134 of the cap, or on only one of the walls.

Because of this taper, the cap will have to be introduced into the track from the correct (wider) end, with the correct (narrower) end of the cap leading. As the cap moves along the track, the taper will force the joint faces 123,136 into contact. Both these faces will be machined flat. As the cap moves into the track, there will also be increasing contact between the walls 132 and 134 and ultimately the engagement will be such that the cap can move no further along the track. At this point, the joint faces 123,136 will be in close contact and the walls 132,134 will jam against one another to secure the cap in place. The engagement between the walls 132 and 134 will be in the nature of an interference fit, and an unmachined (eg as-cast) finish to one or both of these surfaces will be adequate to locate and lock the cap.The two semi-circular bearing surfaces will thus be aligned properly, not only on original assembly, but also after removal and subsequent reassembly.

Figure 4 shows an alternative form of dovetail engagement where the walls 232,234 are no longer flat but have a curved form, and where the top edges of the track 230 are relieved at 231. These shape changes are the sorts of changes which can be considered to relieve stresses arising in use, and to ease manufacturing.

The figures show a single bearing housing assembly. In practice there are likely to be at least two and possible more bearing housings to provide the bearings for a single shaft.

Although this description of the invention makes specific reference to camshaft bearings for motor vehicle internal combustion engines, the invention is not limited to this application. The invention can be used with other bearing assemblies, although it is likely to be necessary to have sufficient space in an axial direction to one side of the track 130 to allow the cap to be lined up and introduced into the track.

The invention can be used with similar or dissimilar metals for the cap and mating part, and results in a good bearing housing assembly which requires considerably less machining/drilling of components before assembly than was hitherto necessary. The invention also makes it possible to reduce the space occupied by a bearing housing assembly.

Claims

1. A bearing housing comprising a bearing cap and a mating part, wherein the cap and the mating part are secured together by a sliding joint assembled by relative movement between the cap and mating part in a direction parallel to the bearing axis.

2. A bearing housing as claimed in Claim 1, wherein the sliding joint is a dovetail tenon arrangement.

3. A bearing housing as claimed in Claim 2, wherein the mating part has an undercut track formed in the casting of the mating part, and the cap has a correspondingly shaped tenon which slides into the undercut track.

4. A bearing housing as claimed in any preceding claim, including means for securing the cap and mating part against further sliding movement.

5. A bearing housing as claimed in Claim 5, wherein the cap and the mating part have matching axial tapering forms, so that they jam together when the desired extent of sliding movement has taken place.

6. A bearing housing as claimed in any preceding claim, wherein the mating part and the cap are castings which are machined on their semi-circular faces and on their faces adjacent and on either side of the semi-circular faces, but are otherwise 'as-cast'.

7. A bearing housing as claimed in any preceding claim, wherein the cap has a head with a domed contour which approximately follows the contour of the semi-circular recess.

8. A method of assembling a bearing housing1 wherein a bearing cap is slid axially of the bearing axis into an undercut region of a mating part, to form a bearing housing between the cap and the mating part.

9. A bearing housing substantially as herein described with reference to the accompanying drawings.