Abstract:
The invention relates to a sliding bearing element comprising a supporting layer, an aluminum alloy-based intermediate layer, and an aluminum alloy-based bearing metal layer. The aluminum alloy composition of the intermediate layer includes at least the following components in percent by weight: 3.5 to 4.5 of copper; 0.1 to 1.5% of manganese; 0.1 to 1.5% of magnesium; and 0.1 to 1.0% of silicon.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates to a plain bearing element having a support layer, a preferably lead-free intermediate layer based on an aluminum alloy, and a preferably lead-free bearing metal layer based on an aluminum alloy. 
     2. Related Art 
     Such bearings are the subject of numerous documents. For example, reference is made to unexamined German applications EP 0 672 840 A2, EP 1 522 750 A1 or U.S. Pat. No. 5,470,660. The plain bearing element in the form of a bearing shell has a support shell made of steel on which a foil-like bearing metal layer or antifriction layer is applied by roll plating. Since the aluminum-based bearing metal layer that generally contains a high amount of tin cannot be plated to the steel support layer with sufficient adhesion, the bearing metal layer is initially plated with an intermediate layer by means of roll plating to form a foil laminate. Initially, an intermediate layer of pure aluminum was used that enables strong adhesion to the steel support layer. This foil laminate is then applied to the steel protective layer in several rolling steps with or without intermediate heat treatment while reducing the thickness of the layers. The finished laminate is then processed by being stamped or cut into plates and, depending on the finished product, processed into a radial bearing by bending or roll forming. 
     The aforementioned documents are based on the knowledge that the adhesion of the aluminum-based bearing metal layer to the steel support layer can be improved, yet the material properties of the pure aluminum intermediate layer do not ensure that the laminate has sufficient fatigue strength during operation. Consequently, EP 0 672 840 A2 proposes forming an intermediate layer based on a hardenable aluminum alloy, possibly with safety running features instead of pure aluminum foil. The hardness of the intermediate layer formed in this manner is adjusted to a value of approximately 68 HV 0.5 and is therefore higher than the hardness of the anti-friction layer that is approximately 35 to 40 HV 0.5. The hardness which decreases in the direction of the bearing metal layer or antifriction layer is intended to have a positive effect on the fatigue strength and hence on the durability and the life of the plain bearing. 
     U.S. Pat. No. 5,470,666 arrives at a similar result. In this case as well, the hardness increases from the plain bearing layer over the intermediate layer to the metal support layer, and the hardness of the intermediate layer is adjusted to lie between 25 HV and 60 HV. The thickness of the intermediate layer is 50 to 90% of the overall thickness of the bearing metal layer and the intermediate layer. The intermediate layer is therefore at least as thick or significantly thicker than the bearing metal layer. The intermediate layer is formed of an aluminum alloy with a total of 0.3 to 5 weight percent of alloy components selected from the group consisting of Mn, Cu, Zn, Si, Mg and Fe. The upper limit of the intermediate layer hardness of 60 HV is determined by the formability that is required to compensate for edge bearing, that is, an unavoidable misalignment between the shaft and bearing axis. 
     SUMMARY OF THE INVENTION 
     The inventors have, however, found that deformation in the intermediate layer arises with the known bearings under high, specific loads during operation that is enough to displace the intermediate layer material in an axial direction. The intermediate layer is more or less pressed axially out of the end faces of the intermediate bearing shells. This phenomenon is schematically portrayed in  FIG. 2 . An axial section of the plain bearing shell according to the prior art is in the primary load area (for example close to its crest), A steel support layer  20  is on its radial exterior on top of which is an aluminum-based intermediate layer  22 , on top of which is a bearing metal layer  24 . Due to the high specific loads arising in particular in the main load area, the intermediate layer  22  begins to flow in an axial direction (similar to roll plating) and is pressed out of the bearing beyond the axial end face  26  of the steel support layer  20 . The bearing metal layer  24  is partially squeezed out of the bearing along with the intermediate layer  22 . The bearing metal and the connection between the bearing metal and support layer remains undamaged and does not manifest any functional failure. However, close to the end face  26 , cracks  28  are discernible between the steel support layer  20  and the intermediate layer  22 . In conjunction with the squeezed out material of the bearing metal layer and intermediate layer, these enhance the risk of release and hence a total failure of the bearing as operation continues. 
     An object of the invention is therefore to improve the laminate having a bearing metal layer and an intermediate layer, both based on an aluminum alloy, and the steel support layer to largely avoid plastic material deformation in the above-described manner. 
     The plain bearing element according to the invention that in particular is designed in the form of a bearing shell with a support layer, an intermediate layer based on an aluminum alloy and a bearing metal layer based on an aluminum alloy, is characterized in that the aluminum alloy of the intermediate layer has a composition comprising at least the components of 3.5 weight % to 4.5 weight % copper, 0.1 weight % to 1.5 weight % manganese, and 0.1 weight % to 1.5 weight % magnesium. 
     In particular given the high amount of copper, the hardness of the intermediate layer can be adjusted without sacrificing the strength of the bond with the support layer preferably made of steel. The hardness is adjusted during a roll plating process and using suitable heat treatment before and/or during and/or after roller passes. 
     The thickness d 2  of the intermediate layer of the plain bearing element rolled to a final dimension is preferably 30 μm to 250 μm and, depending on the wall thickness of the bearing shell, 50 μm to 250 μm, especially preferably 80 μm to 175 μm, and most preferably 150 μm to 175 μm. 
     The inventors have found that an intermediate layer of this thickness with the aforementioned composition having a comparably high hardness is suitable on the one hand to achieve sufficient plastic compliance and hence sufficient formability. On the other hand, a high, adjustable hardness in conjunction with the comparably thick intermediate layer can ensure that the intermediate layer material is only slightly pressed out of the laminate despite plastic deformation. 
     The intermediate layer therefore preferably has a microhardness of 70 HV 0.01 to 110 HV 0.01, and particularly preferably 85 HV 0.01 to 100 HV 0.01. 
     The Vickers hardness test of the intermediate layer of the finished (shaped) plain bearing elements follows the European standard EN 6507-1. The test tip (of the penetrating body) is pressed into the intermediate layer in the plane direction in the area of a prepared cut edge of the plain bearing element. The cut edge is preferably prepared by being ground. 
     The aluminum alloy of the intermediate layer preferably has 0.1 to 1.0 weight % silicon. This increases the strength of the aluminum alloy. 
     The aluminum alloy of the intermediate layer also preferably has (in weight %): Iron 0.05% to 1.0%, chromium and 0.05% to 0.5%, and zinc 0.05% to 0.5%. 
     Most preferably, the aluminum alloy of the intermediate later has (in weight %): Manganese 0.4% to 1.0%, magnesium 0.4% to 1.0%, and silicon 0.2% to 0.8%. All of these alloy elements are for increasing the strength and hardness of the material. 
     It is also advantageous when the aluminum alloy of the inter mediate layer has a total of 0.05 to 0.25% zirconium and titanium (in weight %). 
     In particular, the aluminum alloy of the intermediate layer advantageously does not have more than 0.1 weight %, and a total of 0.25 weight %, of other alloy components than the aforementioned. 
     The thickness d 3  of the bearing metal layer of the plain bearing element is preferably 150 μm to 400 μm, and especially preferably 200 μm to 400 μm. 
     The bearing metal layer preferably has an aluminum alloy with 1.0-3 weight % nickel, 0.5-2.5 weight % manganese, 0.02-1.5 weight % copper, a soft phase component of 5-20 weight %, the usual permissible impurities, with the rest being aluminum. The soft phase component is especially preferably 8-12 weight % with reference to the entire aluminum alloy. For example, an AlSn11.5 Ni1.5 Cu0.6 mN0.6 alloy is suitable for the bearing metal layer. 
     Tin and/or bismuth are preferable as the soft metal components of the bearing metal layer. 
     The Brinell hardness of the bearing metal layer, especially in one of the aforementioned compositions, is preferably adjusted to 50-70 HBW 1/5/30, and especially preferably 50-60 HBW 1/5/30. 
     Between the intermediate layer and the bearing metal layer and/or between the intermediate layer and the support layer, there is preferably a roll plating bond. 
    
    
     
       THE DRAWINGS 
       Additional objects, features and advantages will be further explained in the following with reference to an exemplary embodiment using the drawings. The following are shown: 
         FIG. 1A  perspective section of an exemplary embodiment of the plain bearing element according to the invention in the form of a bearing shell; 
         FIG. 2  An axial cross section in the crest area of a bearing shell according to the prior art after experiencing a load; 
         FIG. 3  An axial cross section in the crest area of a bearing shell according to the invention after experiencing a load; 
         FIG. 4  A curve of the pressure profile in the peripheral direction along a loaded bearing shell during first use; 
         FIG. 5  The pressure profile curve in a peripheral direction along the bearing shell under the same load as in  FIG. 4 , but after plastic deformation; 
         FIG. 6  The pressure profile curve in an axial direction in the area of maximum load on the bearing shell during first use; 
         FIG. 7  The pressure profile curve in an axial direction in the area of maximum load of the bearing shell after plastic deformation, and 
         FIG. 8  The plastic compliance of an exemplary embodiment of the bearing shall according to the invention in the area of maximum load in hand axial direction depending on the material or hardness and thickness of the intermediate layer. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows the basic design of a bearing shell according to the invention having a support layer  10  that preferably consists of steel. An intermediate layer  12  and a bearing metal layer  14  are plated in this sequence onto the support layer  10 . The bearing surface  16  is formed on the inside of the bearing metal layer  14  and that is in direct sliding contact with a counterrotating element such as a shaft (not shown). The shaft lies (directly) on the bearing surface  16  and exerts radial pressure on the plain bearing element. The plain bearing element is typically lubricated with oil so that an oil film builds up between the shaft and the bearing surface under hydrodynamic pressure due to the rotation of the shaft, and this prevents the shaft and bearing layer from directly contacting. 
     For production reasons, the intermediate layer  12  and the bearing metal layer  14  can be plated beforehand into a two-layer laminate both they are plated onto the steel support layer  10 . After being plated onto the steel support layer  10 , the thickness d, of the inter mediate layer of the plain bearing element according to the invention is 50 μm to 250 μm, and preferably 150 μm to 175 μm. The thickness d 3  of the bearing metal layer is 200 μm to 400 μm and preferably 250 μm to 350 μm. 
       FIG. 3  shows a section in the axial direction in the peripheral area of the greatest load on a plain bearing element according to the invention after being subject to a typical load. In comparison with  FIG. 2 , one can see that both the intermediate layer  32  plated directly onto the steel support layer  30  as well as the bearing metal layer  34  plated onto the intermediate layer  32  were only slightly squeezed out of the plain bearing element in an axial direction. Both the roll plating bond  36  between the steel support later  30  and the intermediate layer  32  as well as the roll plating bond  38  ideally remain intact so that, in comparison to the known bearing in  FIG. 2 , a substantial reduction is anticipated of the risk of the layers releasing along with the total failure of the bearing under the same load. 
       FIG. 4  shows the pressure profile in an initial typical load situation of a new, i.e., not plastically deformed, radial bearing element in a peripheral direction indicated by arrow  40 . An axial section of the same bearing in the same situation is shown in  FIG. 6 , i.e., along the width of the bearing (arrow  60 ) in the peripheral area of the largest load. In  FIG. 4 , one can see a significant maximum pressure in the area of the crest identified by the dot-dashed line  42 . The pressure is distributed over a comparatively narrow angular range in the peripheral direction. The pressure is distributed unevenly in the direction of the bearing width  60  such that two significant maximum pressures  62 ,  64  arise in the axial end areas (see  FIG. 6 ). These reflect so-called edge bearings that are caused by a load-related sag in the counterrotating elements (the shaft or the shaft journal) and/or by load-related deformation of the bearing housing. The high specific loads represented by the pressure peaks cause premature material fatigue and finally premature total failure of the plain bearing. 
     To improve the durability of the plain bearing, the intermediate layer is designed according to the invention so that it possesses sufficient plastic deformability that reduces the pressure peaks after a certain run-in phase. This state is shown in  FIGS. 5 and 7 . In direct comparison with  FIG. 4 , one can see in  FIG. 5  that, after the run-in phase, the pressure is distributed over a longer peripheral section, and the maximum pressure is less at the crest  42 . Due to the deformability of the intermediate layer under an operating load, the oil film pressure is redistributed, as it were, in the gap between shaft and the plain bearing element. This effect can be seen even more strongly along the width of the bearing in  FIG. 7 . The bearing is plastically deformed in the axial end sections such that a part of the pressure is redistributed to the axial middle area. The maximum pressures  72  and  74  are flattened to the benefit of an increase the pressure in the area of the minimum  76 . Overall, the specific bearing load is the same, but there are no areas with a dangerously excessive specific load, and the anticipated fatigue of the bearing material is after a much longer exposure to a load. 
       FIG. 8  shows the plastic compliance, i.e., the deformability of plain bearing elements according to the invention in comparison with known plain bearing elements in the direction of the (half) bearing width. The curve is shown starting from the middle of the plain bearing at 0 in an axial direction up to the axial end of the plain bearing at 9. The thick, continuous line “A” indicates the plastic compliance of a laminate according to the prior art based on a 75 mm thick intermediate layer consisting of an Al—Mn1-Cu alloy (EN AW-3003) with a hardness of 60 HV 0.01. Such a layer has the necessary compliance for improving the long-term strength as mentioned at the beginning. However, when this intermediate layer material is used, one observes that it is squeezed out as explained with reference to  FIG. 2 . Just increasing the thickness of the intermediate layer with the same material yields excessively high plastic compliance as the thick dotted line “B” shows with a significant minimum of approximately 6.7. Increasing the thickness of the intermediate layer by itself does not prevent the inteiinediate layer material from squeezing out of the laminate. 
     The latter is only achieved by using an aluminum alloy for the intermediate layer having 3.5 weight % to 4.5 weight % copper, and after roll plating and possibly heating to a microhardness of 70 to 110 HV 0.01 and preferably 85 to 100 HV 0.01. Plain bearing elements having this intermediate layer material and difference intermediate layer thicknesses were investigated, and an intermediate layer thickness between 50 μm and 250 μm proved to be quite suitable for achieving the desired plastic compliance. Particularly preferable are immediate layer thicknesses between 150 μm (see line “D”) and 200 μm (see line “C”), and most preferably between 150 μm and 175 μm (see line “E”).