GB2442969A

GB2442969A - Friction bearing

Info

Publication number: GB2442969A
Application number: GB0620707A
Authority: GB
Inventors: Ian Graham Pegg
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2006-10-19
Filing date: 2006-10-19
Publication date: 2008-04-23
Also published as: GB0620707D0; DE102007048500A1

Abstract

A liquid lubricated friction bearing comprising opposed and relatively movable first and second bearing surfaces 10', and a liquid passageway in one of the surfaces for allowing liquid to flow between the surfaces 10', wherein at least one of said surfaces 10' is textured so as to create areas of localised higher pressure within the liquid, such that the relative motion, acting on the liquid, generates a pressure forcing the bearing surfaces 10' apart. The textured surface 10' includes elongate pockets 20' each inclined relative to the direction of relative motion of the bearing surfaces 10' in such a manner as to deflect liquid lubricating the surfaces 10' away from the edges 18' and towards the centre line of the bearing. The pockets may unite in the centre to form chevron shaped pockets 20'.

Description

Friction Bearing This invention relates to liquid lubricated friction

bearings, and more particularly, to surface textured bearings for improved load bearing and increased lubricant retaining properties.

NO 2004/063533 discusses in detail the advantages of laser surface texturing (LST) of bearing surfaces in order to improve the performance of liquid film bearings. The disclosure specifically relates to thrust bearings but is equally applicable to radial bearings such as those used to support the connecting rods and crankshaft in internal combustion engines.

The above disclosure, incorporated herein by reference, teaches how, by forming micropores into the opposing surfaces of the bearing, pockets of high pressure are created within the oil film. This high pressure serves to force the bearing surfaces apart which leads to reduced wear and also to reduced levels of friction.

Lasers are used to produce the pockets that constitute the texturing of the surface. The pockets can therefore, be very accurately located, and their shape, size area density well controlled.

Oil film bearings require constant replenishment of the oil as the load pressure on the bearing tends to squeeze the oil out from between the bearing's opposing surfaces. Oil is therefore pumped into the bearing to maintain a high pressure between the bearing surfaces. By reducing the rate at which oil is expelled from the bearing, the load on the supply sump would also decrease. This would allow the use of a smaller oil pump and reduce the pumping losses that an engine driving the pump has to overcome.

With this aim in mind, the present invention provides a liquid lubricated friction bearing comprising: opposed and relatively movable first and second bearing surfaces, and a liquid passageway in one of the surfaces for allowing liquid to flow between Lhe surfaces, wherein at least one of said surfaces is textured so as to create areas of localised higher pressure within the liquid, such that the relative motion, acting on the liquid, generates a pressure forcing the bearing surfaces apart, characterised in that a textured ic surface includes elongate pockets each inclined relative to the direction of relative motion of the bearing surfaces in such a manner as to deflect liquid lubricating the surfaces away from the edges and towards the centre line of the bearing.

Both surfaces may be textured.

Advantageously, the texturing of both surfaces may include elongate pockets each having a long axis pointing from an edge towards the centre line of the bearing, and in the direction of liquid flow relative to each the respective surface.

Preferably, pockets adjacent both edges located on opposing sides of the centre line of the bearing are joined at the centre line to form chevron shaped pockets pointing in the direction of liquid flow.

Advantageously wherein the pockets are made by a laser.

Alternatively the pockets are made by a mechanical press.

As another option the pockets may be stamped out using a textured roller.

In a preferred embodiment, secondary pockets may be provided adjacent the centre line of the bearing.

Further preferably, the secondary pockets may be S elongate in shape and have a long axis substantially perpendicular to the centre line of the bearing.

Preferably the liquid used is oil.

The invention will now be described further by way of example with reference to and as illustrated in the accompanying drawings in which: Figure 1 is a plan view of a bearing surface showing the pockets as described by an embodiment of the present invention, Figure 2 is also a plan view of a bearing surface showing chevron shape pockets according to another embodiment of the present invention, Figure 3 is a magnified view of the dotted circle labelled A in Figure 1, Figure 4 is a plan view of a conventional bearing surface showing the localised movement of oil, Figure 5 is a plan view of the bearing surface of figure 1 showing the localised movement of oil, Figure 6 is a three dimensional view of a rotating bearing surface showing the same pockets as described by the present invention, and Figure 7 is a three dimensional view of the bearing surface of Figure 1.

Figure 4 shows the conventional flow of lubricating liquid, in this case oil, inside a hearing. Friction bearings work by placing a softer metal bearing shell, in contact with a harder usually steel rotating element having a bearing surface for rotating relative to the bearing shell, for example, a crank shaft rotating within a pillow block of a crank case, or inside the big end of a connection rod. Oil is usually fed either through the bearing shell or through the bearing surface of the rotating element to occupy the space between the two bearing surfaces to allow them to slide relative to one another.

Immediately adjacent the first bearing surface 10, the oil film tends to he stationery due to friction with the surface. As distance from the surface increases the layers of oil film sheer, allowing them to slip relative to one another. The furthest oil layer, adjacent the opposing bearing surface 26 is stationery relative to that surface, but moving fastest relative to the first bearing surface 10.

The oil therefore has an average velocity across the thickness of the bearing surface and the direction of that oil relative to the surface is shown in each figure by an arrow labelled 12.

Oil is supplied through an oil supply hole fed by an oil gallery (not shown) into the space between the surfaces along the centre line of the bearing (shown in the figures as a straight dotted line), equidistant from the outer edges 18". The oil is driven around the circumference by the friction between the rotating axle (e.g. the crank shaft) and the adjacent oil layer, and by friction between adjacent layers. Oil tends to flow along the centre line of the bearing and toward the edges 18" of the bearing due to the high hydraulic pressure along the centre line of the bearing surfaces and the low to zero pressure at the edges 18".

It has been shown, in WO 2004/063533 that pockets in the bearing surfaces, cause localised regions of high oil pressure in a similar way to those created by the surface of a golf ball. Higher oil pressure is created hydro-dynamically, i.e. by movement of the oil relative to the surface 10 and the pockets 16. The high pressure serves to force the bearing surfaces 10 and 26 apart making the bearing perform better with lower friction.

In the present invention, shown principally in figure 1, the inventor has recognised that the regions of higher pressure as well as forcing the bearing surfaces apart, can he used to reduce the egress of oil from the bearing (see figure 5 cf. figure 4) . By using elongate pockets 14 "pointing" toward the centre line of the bearing surface 10 (and 26 in figure 6), oil tending to flow toward the outer edges 18 of the bearing surfaces meets a high pressure region and is deflected around it. The position and is shape of the pockets is such that it is directed back toward the centre line.

The result is that a smaller flux of oil through the bearing may be used to maintain the separation between the bearing surfaces, therein reducing the load on an oil pump used to provide a feed of oil to the bearing.

Figure 3 shows in details the dotted circle in figure 1, labelled A. The arrows in the figure show the localised movement of oil as it approaches the elongate inclined pocket 14. As is shown, some oil will escape the bearing surface 10 from the edge 18, but a significant portion will be redirected back into the bearing by the high pressure region associated with pocket 14. This is only possible due to the inclination of the pocket with respect to the direction of oil flow 12 relative to the surface 10.

In figure 2, another embodiment shows the use of chevron shaped pockets 20' to achieve a similar effect to the pockets 14 and 16 of figure 1. Here oil flow 12 along the centre line of the bearing surface 10' has no option other than to pass directly over the pockets, creating localised higher pressure areas that force the bearing surface 10' and the opposing bearing surface 26 (not shown in this figure) apart. Again, much of the oil flowing s towards the edges 18' of the bearing surface 10' is deflected back toward the centre line.

Returning to preferred embodiment, figure 5 clearly shows the small scale flow of oil around the pockets 14. The central pockets 16 are not shown here as they do not affect the circumferential flow, they merely impart a radial bearing surface separating force.

Figures 6 and 7 show the position of the pockets 14 and is 16 in three dimensions. These figures show how the pockets are applied to the curved surfaces which rotate relative to one another. Figure 6 shows a crankshaft main bearing journal 22. Arrow 24 indicates the direction of rotation of the shaft. It is clear that the inclined elongate pockets 14 are arranged in the opposing direction to the corresponding pockets on the face of the bearing shell shown in figure 7.

This is because the crankshaft 22 is providing the rotation, meaning that the average speed of the oil surrounding it is lower than the speed of rotation due to drag on the oil from the stationery bearing surface lOa. Thus at the surface of the crankshaft, the direction of oil flow 12, is in the opposite direction to its rotation.

Similarly in figure 7, the bearing shell remains fixed to the crank case main bearing pillow block (not shown) . Due to drag on the spinning crank shaft, the average speed of the oil flow is greater than that of the stationery bearing surface 10. The direction 12 of the flow of oil relative to the bearing surface 10, is therefore the same as the direction of crank shaft rotation.

By arranging the pockets 14 and 16 on the opposing bearing surfaces in this way, both sets of pockets respectively contribute to the reduction of oil loss from the edges of the surtaces and to the separating force b reducing the friction in the bearing.

Claims

Claims 1. A liquid lubricated friction bearing comprising: opposed and

relatively movable first and second bearing S surfaces (10, 26) , and a liquid passageway in one of the surfaces for allowing liquid to flow between the surfaces, wherein at least one of said surfaces is textured (16) so as to create areas of localised higher pressure within io the liquid, such that the relative motion, acting on the liquid, generates a pressure forcing the bearing surfaces apart, characterised in that a textured surface includes elongate pockets (14) each inclined relative to the direction of relative motion of the bearing surfaces in such a manner as to deflect liquid lubricating the surfaces away from the edges (18) and towards the centre line of the bearing.
2. A bearing as claimed in any claim 1, wherein both surfaces are textured.
3. A bearing surface as claimed in claim 2, wherein the texturing of both surfaces includes elongate pockets each having a long axis pointing from an edge towards the centre line of the bearing, and in the direction of liquid flow relative to each the respective surface.
4. A bearing as claimed in any preceding claim, wherein pockets adjacent both edges located on opposing sides of the centre line of the bearing are joined at the centre line to form chevron shaped pockets pointing in the direction of liquid flow.
5. A bearing as claimed in any preceding claim, wherein at least some of the pockets are made by a laser.
6. A bearing as claimed in any preceding claim, wherein at least some ol the pockets are made by a mechanical press.
7. A bearing as claimed in any preceding claim, wherein at least some of the pockets are made by a textured roller.
8. A bearing as claimed in any preceding claim, wherein secondary pockets are provided adjacent the centre line of the bearing.
9. A bearing as claimed in claim 8, wherein the secondary pockets are elongate in shape and have a long axis substantially perpendicular to the centre line of the bearing.
10. A bearing as claimed in any preceding claim, wherein the liquid is oil.
11. A bearing substantially as herein described with reference to all but figure 4 of the accompanying drawings.