GB2378484A

GB2378484A - Camshaft & bearing arrangement comprising an axial position locating means

Info

Publication number: GB2378484A
Application number: GB0114305A
Authority: GB
Inventors: David Ian Thompson
Original assignee: Ricardo Consulting Engineers Ltd
Current assignee: Ricardo PLC
Priority date: 2001-06-12
Filing date: 2001-06-12
Publication date: 2003-02-12
Anticipated expiration: 2021-06-12
Also published as: GB0114305D0; GB2378484B

Abstract

An automotive camshaft 2 comprises a bearing base 6 and a cap 12, each of which define semi-circular recesses 8, and wherein the bearing cap 12 is secured to the bearing base 6 so as to define a hole through which a portion 4 of shaft 2 can be rotatably received, and wherein either base 6 or cap 12 carries a locating peg 13 which projects from the surface of the respective recess in to a circumferential recess 14 of shaft 2. Shaft 2 may be hollow (as in Fig 3) and as such allows the flow/supply of lubricant through it so as to lubricate the shaft. Alternatively, in an arrangement where the shaft is solid (as in Fig 4), then locating peg 13, connected to oil passage (22) acts as a lubricant supply. Peg 13 may be made from hardened steel, carbide, silicon nitride or a sintered material.

Description

ROTARY SHAFT BEARINGS The present invention relates to rotary shafts and their bearings and is concerned with rotary shafts of the type which are mounted in one or more bearings comprising a bearing base which defines a recess of semicircular cross-section, and a bearing cap which is secured to the bearing base and also defines a recess of semicircular cross-section, the two recesses together defining a hole of circular cross-section in which a portion of the shaft is rotatably received.

Such rotary shafts are used in a wide variety of applications, for instance as overhead camshafts in automotive engines. Overhead camshafts are rotated, typically via a drive train by the engine crankshaft, in order to open and close the inlet and exhaust valves of the engines at the appropriate times. The camshaft drive train frequently includes a helical gear arrangement and this not only rotates the camshaft but also applies an axial load to it. An axial load can also be applied to the camshaft by the sliding engagement of the cams on the surface of the rocker arms, which is frequently not truly parallel to the axis of the camshaft. In order to resist this axial load, camshafts are provided with a thrust bearing assembly, which typically comprises a ground or turned flange on the camshaft which is received in a milled slot in the cylinder head.

However, if roller rockers are used in the engine and the camshaft is not driven by a helical gear arrangement, the axial thrust on the camshaft is in fact extremely small. It is nevertheless usual to provide a thrust bearing, e. g. of the type referred to above. However, the thrust bearing absorbs very little thrust

and acts more as a guide or location feature.

The invention is based on the recognition that the thrust bearing provided in such shafts is relatively expensive but in many cases is largely unnecessary and that the location function of the thrust bearing could be performed very much more simply and cheaply. It is, therefore, the object of the invention to provide a shaft mounted in a bearing of the type referred to above which is provided with axial location which is cheaper and simpler than the known thrust bearing constructions.

According to the present invention, a rotary shaft of the type referred to above is characterised in that one of the bearing base and the bearing cap carry a locating member which projects from the surface of the respective recess and the said portion of the shaft affords a circumferential recess into which the locating member extends.

Thus the rotary shaft in accordance with the invention need not have a projecting annular flange or the like, as is common and the shaft is restrained axially by a locating member, such as a peg, which extends inwardly from the surface of the journal bearing into a circumferential slot in the portion of the shaft accommodated within the bearing. Although the cooperating peg and slot are not able to resist substantial axial loads, this is frequently not necessary.

Since there is no necessity to provide a locating flange on the camshaft, the maximum dimensions of the camshaft, both before and after machining, are reduced, both in the direction of its length and in the radial direction. It is very much cheaper and simpler to machine a circumferential slot into the shaft than to machine the two opposed faces of a locating flange. The formation of the

necessary hole, e. g. by drilling, is a simple matter and the cost of a locating member, which is inherently very small, is low. Accordingly, the arrangement in accordance with the invention is significantly cheaper than the known thrust bearing. Furthermore, the provision of the circumferential groove means that a smaller area of the surface of the shaft is in sliding contact with the internal surface of the bearing and this results in reduced frictional losses.

In the preferred embodiment, a hole is formed in the surface of the recess of either the bearing base or the bearing cap and the locating member comprises a peg secured within the hole. This peg may be solid or alternatively it may be of hollow and open-ended construction and the hole in the surface of the recess forms part of an oil supply passage. Thus in this event the peg may constitute the lubricant supply path to the bearing.

The locating peg may be of constant cross-section over its length. However, if the magnitude of the axial thrust on the shaft is more than a nominal value or if the wear of the head of the peg in contact with the side surfaces of the circumferential recess in the shaft is excessive, the peg may have a head whose area is larger than that of the shaft of the peg. In this event, the head of the peg may have two elongate side surfaces opposed to the side surfaces of the recess in the shaft. These two side surfaces may be connected by arcuate end surfaces.

The tapering spaces between the arcuate end surfaces and the side surfaces of the recess in the shaft will act as a"lead-in"for lubricating oil.

Further features and details of the invention will be apparent from the following description of certain specific embodiments which will be described below in more detail with reference to the accompanying diagrammatic drawings, in

which: Figure 1 is a perspective exploded view of a rotary shaft in accordance with the invention from which the bearing cap has been omitted for the sake of clarity; Figure 2 is a side view, partly in section, of the rotary shaft and bearing shown in Figure 1; Figure 3 is a transverse view, partly in section, showing a solid locating peg; Figure 4 is a view similar to Figure 3 of a modified embodiment in which the locating peg is hollow; and Figure 5 is a perspective view of an alternative construction of the locating peg.

Figures 1 and 2 show part of an overhead camshaft 2 in an automotive engine.

The camshaft has a number of portions of increased diameter 4, each of which is received and enclosed by a respective journal bearing. Each bearing comprises a bearing base 6, which in this case constitutes a rib integral with and upstanding from the cylinder head. The bearing base affords an upwardly open recess 8 of circular cross-section, that is to say a semi-cylindrical recess.

Secured to the bearing base 6 by two bolts 10 is a bearing cap 12, which also affords a recess of circular cross-section (not shown). When the bearing cap is connected to the bearing base, the two semicircular recesses constitute a circular hole in which the portion 4 of increased diameter of the shaft 2 is accommodated.

Formed in the centre of the surface of the recess 8 is a hole in which a solid circular peg 14 is secured. Formed in the portion 4 of increased diameter of the shaft 2 is a circumferential recess or groove 14 whose width is slightly greater than the diameter of the peg 12.

In use, the bearing base and bearing cap together constitute a journal bearing which receives and retains the rotating shaft 2. If an axial force should act on the shaft 2, thereby tending to cause it to move in the axial direction, such axial movement is restrained by the engagement of the peg 12 against the side surfaces of the groove 14.

In the embodiment shown in Figure 3, the shaft 2 is of hollow tubular construction and its interior constitutes an oil supply conduit. The oil is supplied to the bearing through apertures or drillings in the shaft 2, such as that indicated by reference numeral 18.

In the alternative construction shown in Figure 4, the shaft 2 is solid and the peg 12 is of open-ended hollow construction. The hole 20 in which it is secured communicates with an oil supply passage 22 through which oil is supplied to the bearing. It is therefore not necessary to provide an oil supply passageway in the shaft 2.

In the embodiments described above, the locating peg 12 is of constant crosssection over its length and its outer side surface is in sliding engagement with one or other side surface of the groove 14 in the shaft 2. If, however, significant axial thrust on the shaft is to be expected, the peg 12 may have the construction shown in Figure 5 in which it has a shaft 24 and a head 26, which

is significantly larger than the shaft. The head 26 has two elongate substantially flat side surfaces, which are connected together by two arcuate end surfaces. The overall shape of the head 26, when viewed in the direction of the length of the peg, is therefore generally oval, that is to say rectangular with rounded ends.

In order to ensure that the peg maintains its desired orientation with respect to the circumferential groove 14, the shaft 24 may be splined, whereby rotation in its hole is prevented. Alternatively, the peg may be self-aligning so that it can be a transition fit in the hole.

The locating peg may be made of hardened steel, carbide, silicon nitride or sintered material. The use of sintered material is particularly preferred in connection with the construction of Figure 5.

Whilst the invention has been described primarily in connection with automotive camshafts, it will be appreciated that it can be used in connection with any rotary shaft which is subject to relatively light axial loads.

Claims

CLAIMS 1. An automotive camshaft mounted in a bearing comprising a bearing base, which defines a recess of semicircular cross-section, and a bearing cap, which is secured to the bearing base and also defines a recess of semicircular cross-section, the two recesses together defining a hole of circular cross-section in which a portion of the shaft is rotatably received, one of the bearing base and the bearing cap carrying a locating member which projects from the surface of the respective recess and the said portion of the shaft affording a circumferential recess into which the locating member extends.
2. A camshaft as claimed in Claim I in which a hole is formed in the surface of the recess of the said one of the bearing base and the bearing cap and the locating member comprises a peg secured within the hole.
3. A camshaft as claimed in Claim 2 in which the camshaft is solid.
4. A camshaft as claimed in Claim 2 in which the peg is of hollow and open-ended construction and the hole in the surface of the recess forms part of an oil supply passage.