GB2216199A - Bearing for internal combustion engines - Google Patents

Abstract

A slide bearing particularly for use with internal combustion engines has a backing layer 11, an intermediate layer 12, provided with internal peripheral grooves located crosswise relative to the length of the bearing and longitudinally spaced from each other, and a slide layer 14 of a material which is softer than the material of the intermediate layer and fills the grooved portions. The grooves have a depth and longitudinal spacing with uniform or variable dimensions, at least one of the characteristics of depth (Fig 5) and spacing (Fig 4) being variable. This design allows a selective distribution of harder material and softer material on defined portions of the bearing as a function of specific operating requirements. Preferably, a diffusion or bonding layer 13 is provided in the grooved portions. <IMAGE>

Description

BEARINGS FOR INTERNS COMBUSTION ENGINES This invention relates to bearings for internal combustion engines, particulary to multilayer bearings for high loads, especially such bearings being used in diesel engines As is well known bearings for internal combustion engine are subjected to mechanical loads generated by the pressure of combustion gases on the piston top, which loads are transmitted to the bearings by the connecting rods. These bearings must have the following properties namely resistance to wear caused by friction, resistance to fatigue caused by cyclic loading, embeddability of foreign particles in the engine oil, and conformability to compensate for shaft misaligaments.

Because of the variety of such properties, slidable bearings can be made of different materials for different performances. One wellknown type of bearing is the so-called multilayer bearing made up of a backing plate, generally of steel or aluminium, at least one intermediate layer, generally an aluminium alloy or copper-based alloy, and a bearing, or slidable, layer, generally a copper-tin-lead alloy. A diffusion of bonding layer may be present between the bearing layer and the intermediate layer. It is known, however, that in certain applications, where the bearings are subjected to extremely high loads and friction, such as in current diesel engines, these bearings often have a relatively short service life for the material of the slidable layer, suitable to reduce the friction between the shaft and bearing, has not the resistance to wear and fatigue of a harder material.Moreover a harder material on the slidable layer would cause excessive friction and eventual seizure of the shaft.

With a view to solving these problems, it has been proposed to provide slide bearings with grooves filled with softer material, so as to alternate harder material and softer material in the slidable layer, aiming at better properties of resistance to wear and fatigue.

The concept of grooved bearings is quite old. One of the first descriptions of this solution is disclosed in British patent specification No. 524,128 of July 30, 1940. U.S. patents Nos 2,757,055 of July 31, 1956; 2,971,248 of February 14, 1961, and more recently, U.S. Patent No. 4,400,099 of August 23, 1983, also discloses grooved bearings for use in internal combustion engines. Save for particular details of each of the designs described and illustrated in the patent specifications, all of them have in common a slidable layer alternating harder material and softer material. Another basic feature of these bearings is that the grooves on the harder material have uniform depth and spacing between grooves.

While representing an improvement over conventional plain bearings for certain applications, the aforesaid proposals do not take into account some characteristics of specific engine designs and, accordingly, bearing performance requirements. In other words, the provision of grooves with uniform depth and spacing defines an even distribution of harder material and softer material, thereby importing uniform properties to the bearing regardless of particular requirements of every region of the bearing.

Therefore, it is desirable to provide a multilayer plain bearing in which the above mentioned disadvantages are substantially eliminated.

According to the present invention there is provided a slide bearing of the type comprising a backing layer, an intermediate layer on the backing layer, provided with portions of internal peripheral grooves located crosswise relative to the length of the bearing and spaced longitudinally from each other, a slide layer of a softer material than the material of the intermediate layer and arranged to fill the said grooved portions; wherein the said grooved portions exhibit characteristics of depth and longitudinal spacing defined by a variable and/or uniform pattern, with at least one of the said characteristics being variable.

In one embodiment of a slide bearing according to the present invention the grooved portions are provided at least on part of the peripheral length of the bearing, and the grooved portions are arranged at an angle ranging from Oo to 450 in relation to said radial direction.

A diffusion or bonding layer may be included on the surface of the grooved portions.

Therefore, there is provided a slide bearing having internal peripheral grooved portions crosswise the bearing length, longitudinally spaced apart from one another and whose characteristics of depth and longitudinally spacing are defined by any one variable and uniform condition, at least one of said characteristics is mandatorily variable.

This design enables proper dimensioning of the slide layer on the bearing portions which are more subject to high loads and shaft misalignments.

It also offers a more uniform distribution of pressures on these bearing portions.

Accordingly a multilayer plain bearing has been disclosed having an intermediate layer with grooves formed therein and filled with a bearing or sliding material, wherein a selective distribution of harder material and softer material on selected areas of the bearing is provided as a function of specific bearing operation requirements.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figures 1,2,and 3 are longitudinal cross sectional views of plain bearings provided with grooves of various shapes and arranged with uniform spacing; Figure 4 is a longitudinal cross sectional view of a multilayer plain bearing provided with grooves having uniform depth and variable spacing between grooves.

Figure 5 is a longitudinal cross sectional view of a multilayer plain bearing provided with grooves of variable depths and uniform spacing between grooves; Figure 6 is a longitudinal cross sectional view of a multilayer plain bearing provided with grooves of variable depths and variable spacing between grooves; Figures 7 and 7a are graphs showing the effects of various grooves on the peak pressure on the bearing; Figure 8 is a schematic view showing the deformation, under load, of the material filling the grooves; Figure 9 is a comparative graph of the distribution of pressure on a conventional plain bearing, without grooves, on a known grooved bearing and on the bearing according to the present invention; ; Figure 10 is a schematic view of the load pattern in a bearing and particularly illustrates the angle at which pressure is applied to a conventional plain bearing or a bearing having uniformly spaced apart grooves; Figure 10a is a schematic view similar to Figure 10 including the angle of the pressure region of a plain bearing with grooves having variable depths and spacing; Figure 11 shows the thread angle of the grooves in relation to the transverse axis of the bearing.

Figure 12 is a prespective view of a plain bearing in accordance with present invention provided with grooves along all of its circumferential length; and Figure 13 is a perspective view of a plain bearing in accordance with the present invention provided with grooves only on part of its circumferential length.

Referring more specifically to the drawings, Figures 1,2 and 3 illustrate three different configurations of grooved bearings of the known type, made up of one backing layer 1, one intermediate layer 2 provided with grooves, one diffusion or bonding layer 3, and a bearing or slide material 4 filling the grooves of the intermediate layer 2. In this type of bearing, the depth of the grooves and the spacing between grooves are uniform, thereby imparting uniform properties to the bearing.

Various bearings in accordance with the present invention are shown in Figures 4,5 and 6. In these Figures, a backing layer 11 has deposited thereon an intermediate layer 12 provided with grooves which are filled with slide material 14.

A diffusion or bonding layer 13 may be deposted between the intermediate layer 12 and the slide material 13. In the embodiment depicted in Figure 4, the intermediatelayer grooves have a uniform depth, but the spacing between grooves is variable. In the embodiment illustrated in Figure 5, the depth of the grooves is variable and the spacing between grooves is uniform. In the embodiment of Figure 6, the depth of the grooves and the spacing between grooves are both variable.

The selection of one of these characteristics or a combination of two or three of the embodiments is a function of the specific requirements of the bearing. For instance, on a bearing subjected to high loads it is recommended a higher amount of softer material, i.e., slide material, be provided on the part of the bearing which takes most wear. The same holds true in respect of those portions of the bearing which must compensate for shaft misalignments.

Pressure applied longitudinally of the bearing varies according to a parabolic curve. The insertion of a groove in the bearing causes a change in the pressure curve. If the depth of the groove is greater than the diametric clearance i.e , the clearance between the shaft and the bearing, the pressure curve is changed as shown in the sketch of Figure 7. In such case, at the same time as a pressure valley would be obtained because of the insertion of the groove, two pressure peaks are created which are even higher than the original peak. However, if the depth of the groove is lower that a film of oil between the shaft and the bearing, the resulting curve will change as indicated in Figure 7a.

Thus, the provision of grooves with suitable depths and spacings as a function of specific pressure values allows a more uniform distribution of pressures on the most used portions of the bearing, with a flattening of the oil film pressure peak arising out of the effect of induced elastic deformation of the slide material (Figure 8.) The graph in Figure 9 depicts the distribution of pressure in a plain bearing without grooves, on a conventional grooved bearing and on a grooved bearing in accordance with the present invention.

The concept of the invention also offers the inclusion of a greater angle of the pressure region (Figure 10a) as compared with the corresponding angle of a conventional grooved bearing (Figure 10 ), thereby reducing the cavitation region.

Another important advantage is related to lubricaton: the distribution with a flattening of the pressure peak leads to an increase of the modulus of the pressure derived in respect of the bearing edges, thus giving rise to a greater flow of lubricating oil, thereby reducing oil temperature and maintaining a higher viscosity.

The provision of grooves in a bearing in accordance with the present invention may cover all or a part of the peripheral surface of the bearing, as shown in Figure 12 and 13, respectively. For instance, for certain applications it may be adequate to provide grooves only on defined portions of the bearing, while on the other regions it is important to maintain a conventional structure in order to meet certain requirements.

The grooves are helically formed in the direction of the central axis of the bearing and must be arranged according to an angle ranging from Oo to 450, as shown in Figure 11. It is desirable that this angle be as close as possible to zero. It should be noted that an angle in excess to certain values can be detrimental to the slide layer in operation such as, for instance wiping slide material from the grooves.

Claims (5)

1. A slide bearing of the type comprising a backing layer, an intermediate layer on the backing layer, provided with portions of internal peripheral grooves located crosswise relative to the length of the bearing and spaced longitudinally from each other, a slide layer of a softer material than the material of the intermediate layer and arranged to fill the said grooved portions; wherein the said grooved portions exhibit characteristics of depth and longitudinal spacing defined by a variable and/or uniform pattern, with at least one of the said characteristics being variable.

2. A slide bearing as claimed in claim 1, wherein the grooved portions are provided at least on part of the peripheral length of the bearing.

3. A slide bearing as claimed in claim 1, wherein the grooved portions are arranged at an angle ranging from 0 to 450 in relation to said radial direction.

4. A slide bearing as claimed in any one of the preceding claims, including a diffusion or bonding layer on the surface of the grooved portions.

5. A slide bearing substantially as herein before described with reference to, and as illustrated in, Figure 4, or Figure 5, of Figure 6; and Figures 7 to 13 of the accompanying drawings.