Multi-layer sliding bearing having excellent fretting property

A multi-layer sliding bearing having an excellent anti-fretting property, comprises a back steel layer, and a bearing alloy layer formed on the back steel layer. A film of phosphate having a thickness of 0.1-15 .mu.m is formed on a back surface of the back steel layer, thereby enhancing the anti-fretting property of the bearing. The provision of the phosphate film well compatible with a mating material overcomes damage to the bearing due to fretting in a high-speed range. Therefore, the bearing can fully exhibit a bearing performance even under severe conditions of use in a high-speed, high-temperature and high-load range as typically experienced in a high-performance engine.

FIELD OF THE INVENTION 
This invention relates to a multi-layer sliding bearing, and more 
particularly to a sliding bearing which exhibits excellent bearing 
properties even under severe conditions of use of a recent internal 
combustion engine in a high-speed, high-temperature and high-load range, 
which conditions are due to a compact and lightweight design of the engine 
for fuel-saving purposes and to a high-performance design of the engine. 
BACKGROUND OF THE INVENTION 
In one conventional sliding bearing, a bearing alloy layer of an Al--Sn 
alloy, an Al--Si--Sn alloy, a Cu--Pb alloy or a Cu--Pb--Sn alloy is formed 
on a surface of a steel support or backing metal. In another conventional 
sliding bearing, a coating layer is formed on a back surface of a backing 
metal to cope with fretting. 
With a compact and lightweight design of recent internal combustion engines 
for fuel-saving purposes and also with a high output design thereof, the 
engine is used at a high temperature, high speed and a high load. 
Therefore, a close contact of the bearing portion with a housing fails to 
be maintained, so that damage of the bearing, such as fatigue and seizure 
due to fretting (which means a surface damage developing when a slight 
relative motion is periodically repeated between two contact surfaces), 
has frequently occurred. Particularly with respect to a connecting rod, 
not only the bearing but also the connecting rod itself may be subjected 
to fatigue failure. Therefore, whether or not the conventional sliding 
bearings has an anti-fretting property has become a major problem. 
To overcome these problems, it has been proposed to improve the rigidity of 
the housing, or to increase an interference to enable the bearing to 
follow the deformation of the housing when mounting the bearing portion, 
or to form a film of Cu, Ni, Al or an alloy thereof, or a synthetic resin 
such as PTFE, polyamide and polyethylene, on a back surface of a back 
metal of the bearing so as to improve its compatibility with its mating 
material. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a novel multi-layer sliding 
bearing which is so excellent in anti-fretting property as to meet 
conditions of use in a high-speed, high-temperature and high-load range, 
as typically experienced in a high-performance internal combustion engine. 
According to the present invention, there is provided a multi-layer sliding 
bearing having an excellent anti-fretting property, comprising a steel 
backing layer, and a bearing alloy layer formed on the steel backing 
layer, the steel backing layer having a film of phosphate formed on its 
back surface, and the phosphate film having a thickness of 0.1 to 15 
.mu.m. 
The bearing alloy layer can be composed of an aluminum alloy which is an 
Al--Sn alloy, an Al--Si--Sn alloy, an Al--Pb alloy, an Al--Si--Pb alloy, 
an Al--Zn alloy or an Al--Si--Zn alloy. 
The bearing alloy layer can be composed of a copper alloy which is a Cu--Pb 
alloy or a Cu--Pb--Sn alloy. 
An overlay layer can be formed on a surface of the bearing alloy layer. The 
overlay layer is composed of a lead alloy containing at least one kind of 
2 to 30 wt. % in total selected from the group consisting of Sn, In, Cu 
and Sb. Alternatively, the overlay layer is composed of an aluminum alloy 
containing at least one kind of 2 to 60 wt. % in total selected from the 
group consisting of Sn, Pb, Cu, Sb and Si. 
The phosphate film is composed, for example, of zinc phosphate, calcium 
zinc phosphate, manganese phosphate or iron phosphate. 
The phosphate film has achieved the following effects. 
(1) This film prevents a metal-to-metal contact, and exhibits an excellent 
wear resistance against fine vibrations. (2) Since this film has a 
suitable porosity, it serves to retain lubricating oil therein, and 
therefore dampens the contact between the housing and the bearing portion, 
thereby suppressing the fretting phenomenon. (3) This film reduces the 
coefficient of friction between the two surfaces to thereby restrain a 
temperature rise. 
If the thickness of the above phosphate film is less than 0.1 .mu.m, a 
satisfactory effect is not obtained. In contrast, if this thickness is 
more than 15 .mu.m, the film becomes brittle, and besides the cost is 
increased. 
The friction between two contact surfaces is a phenomenon resulting from 
all of comformability, a scuffing property and adherability between these 
two surfaces. Therefore, such respect that the friction coefficient is low 
means that the comformability between the two surfaces is good, that the 
scuffing property and the adherability are low, and that the amount of 
heat produced is small. The inventors of the present invention have found 
from these that whether or not the anti-fretting property is good can be 
determined by the value of the friction coefficient.

DESCRIPTION OF THE INVENTION 
The present invention will now be described more specifically by way of the 
following Examples: 
EXAMPLE 1 
In order to compare the relation between a load and a coefficient of 
friction, test pieces were prepared from a cold-rolled steel sheet (JIS G 
3141 SPCC) commonly used widely as a back metal layer of a bearing. The 
surfaces of the test pieces were treated with respective phosphates to 
provide samples or test pieces. 
Tests were conducted using Suzuki's friction wear test device (which is of 
the type in which a test piece is fixed whereas a mating material is 
rotated). An induction-hardened material (JIS S55C) was used as a mating 
material for the test piece. Oil of 0.1 cc was coated onto the mating 
material, and a wear test lasting for 4 hours, as well as a starting 
friction test, was conducted. Conditions of the tests are shown in Table 
2, and results of the tests are shown in FIGS. 1 and 2. 
As is clear from FIGS. 1 and 2, all of products of the present invention 
were lower in friction coefficient, and were superior in wear resistance, 
as compared with SPCC. 
EXAMPLE 2 
(a) Powder of a copper-lead alloy and powder of a copper-lead-tin alloy 
were splayed onto surfaces of respective steel strips plated at their 
surface with copper. Then, the powder layers deposited respectively on the 
steel strips were sintered in a reducing atmosphere at temperatures of 
700.degree. to 900.degree. C. for 10 to 30 minutes. Then, each of these 
composite sintered materials was passed between rolls to be rolled, and 
then was again sintered and rolled to form a bimetal. 
(b) An Al--Sn bearing alloy and an Al--Zn--Si bearing alloy were prepared 
by continuous casting, and then each of the cast alloys was cut at its 
surfaces, and then was repeatedly rolled and annealed to be finished into 
an alloy strip of predetermined dimensions. Then, each alloy strip was 
pressure-bonded directly or through an Al intermediate layer to a back 
steel strip to provide a bimetal material. 
(c) Each of the bimetals prepared in the above Steps (a) and (b) was 
pressed and machined into a semicircular bearing portion with a width of 
17 mm, in which an inner diameter of the bearing was 42 mm, and the 
thickness of the bearing alloy was 0.3 mm. 
(d) A chemical treatment was applied to each of the bearing portions 
prepared in the above Step (c), and a film of a respective one of various 
kinds of phosphates, which had a thickness of 2 to 8 .mu.m, was formed on 
a back surface (the back metal side) of the bearing. 
Further, in order to provide test bearings having an overlay on the surface 
of the bearing alloy layer, a surface layer (overlay) of a Pb alloy was 
formed by electroplating on the surface of the bearing alloy layer of some 
of the bearings. Also, a surface layer (overlay) of an Al alloy was formed 
by sputtering on the surface of the bearing alloy layer of some of the 
bearings. Each overlay had a thickness of 20 .mu.m. The various kinds of 
test bearings are shown in Table 1. 
In order to confirm the effect (anti-fretting property) of the phosphate 
film, a comparison test was conducted using an electric-hydraulic fatigue 
test device. 
In the test, the bearing was attached to a connecting rod 1 (which was 
formed by forging steel, and its inner peripheral surface had a surface 
roughness of 6.3 .mu.m) mounted on a fixed shaft 3, and a dynamic tensile 
load (W) applied by oil pressure was repeatedly applied to carry out a 
fretting simulation test, and the amount of change of roughness of the 
back surface of the bearing (2) due to the fretting was observed for 
comparison purposes. The condition of the back surface is shown in Table 
1. The conditions of this test are shown in FIGS. 4A to 4D, and results of 
this test are shown in FIG. 3. Here, such a respect that the amount of 
change of roughness of the back surface of the back metal is small means 
that the amount of wear is small, and therefore means that it has an 
excellent anti-fretting property. 
It will be clearly appreciated from FIG. 3 that all of the products of the 
present invention are smaller in the amount of change of roughness than 
the conventional product, and therefore are excellent in anti-fretting 
property. 
As is clear from the test results in Table 1 and FIGS. 1 to 3, all of the 
sliding bearings of the present invention are superior in anti-fretting 
property to the conventional products, and can fully exhibit a bearing 
performance without damage due to the fretting even under severe 
conditions of use at high speed, high rotation speed, a high load and so 
on, as typically experienced in a recent high-performance engine. 
TABLE 1 
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Kind of test bearings and bearing damage 
Overlay 
Damage to bearing 
Sample 
Phosphate film on 
Bearing alloy layer 
layer 
back surface 
Kind No. bearing back surface 
(wt %) (wt %) 
(fretting) 
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Products 
1 zinc phosphate 
Cu--25Pb Pb--10Sn 
none 
of 2 manganese phosphate 
Cu--25Pb Pb--10Sn 
none 
invention 
3 calcium zinc phosphate 
Cu--25Pb Al--20Sn 
none 
4 iron phosphate 
Cu--25Pb Al--20Sn 
none 
5 zinc phosphate 
Cu--1.5Sn--23Pb 
Pb--10Sn 
none 
6 manganese phosphate 
Cu--1.5Sn--23Pb 
Pb--10Sn 
none 
7 calcium zinc phosphate 
Cu--1.5Sn--23Pb 
Al--20Sn 
none 
8 iron phosphate 
Cu--1.5Sn--23Pb 
Al--20Sn 
none 
9 zinc phosphate 
Al--20Sn--1Cu 
none none 
10 manganese phosphate 
Al--20Sn--1Cu 
none none 
11 calcium zinc phosphate 
Al--20Sn--1Cu 
none none 
12 iron phosphate 
Al--20Sn--1Cu 
none none 
13 zinc phosphate 
Al--4Zn--3Si--1Cu--1Pb 
Pb--10Sn 
none 
14 manganese phosphate 
Al--4Zn--3Si--1Cu--1Pb 
Pb--10Sn 
none 
15 calcium zinc phosphate 
Al--4Zn--3Si--1Cu--1Pb 
Al--20Sn 
none 
16 iron phosphate 
Al--4Zn--3Si--1Cu--1Pb 
Al--20Sn 
none 
Conven- 
17 none Cu--25Pb Pb--10Sn 
*occurred 
tional 
18 none Cu--1.5Sn--23Pb 
Pb--10Sn 
*occurred 
products 
19 none Al--20Sn--1Cu 
none *occurred 
20 none Al--4Zn--3Si--1Cu--1Pb 
Pb--10Sn 
*occurred 
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*"Damage to bearing back surface occurred" means that fine pits and 
projections developed at the surface of the back metal. 
TABLE 2 
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Conditions of Suzuki's test 
Starting .multidot. friction 
Items Wear test test 
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Specific load 
3 & 15 MPa 3 & 15 MPa 
Speed 0.01 & 0.05 m/s 
0.01 & 0.05 m/s 
Time 4 Hr 30 sec. for each of 
activation and stop. 
Repeated 10 times. 
Temperature 
Natural temperature 
Natural temperature 
Lubrication 
SAE 30 of 0.1 ml was 
SAE 30 of 0.1 ml was 
coated at the time of 
coated at the time of 
assembling assembling 
Material S55C S55C 
Hardness Hv 500.about.600 
Hv 500.about.600 
of mating 
material 
Roughness Rmax 1 .mu.m Rmax 1 .mu.m 
of mating 
materiall 
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