JP2005133736A - Bush of copper alloy for automatic transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bush of copper alloy for an automatic transmission that is Pb-free. <P>SOLUTION: This bush of copper alloy for an automatic transmission comprises copper alloy excluding Pb, but including graphite in a slide surface. Graphite particles are exposed by 3 area% or more in the slide surface. Favorable lubrication characteristics are achieved especially in a case of use with surface roughness (Ra) of 1μm or less in the slide surface. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a bush made of a copper alloy for an automatic transmission (hereinafter referred to as A / T), and more particularly to a bush using a copper alloy containing no Pb.

  Automotive A / T bushings include over-drive sun gear rear bush, over-drive sun gear front bush, sun gear rear bush, sun gear Built into A / T as sun gear front bush. Since this bush often repeats GO-STOP and the oil film is not formed, wear resistance and seizure resistance under boundary lubrication conditions are important.

  Conventional copper alloys used for A / T contain about 10 to 20% or more of Pb, which is an environmental pollutant, and impart wear resistance with hard particles.

Prior art relating to sintered copper alloys will be described.
According to Patent Document 1 concerning sintered oil-impregnated bearings, Fe: 20 to 64 wt%, Cu: 27 to 59 wt%, Zn: 6 to 24 wt%, Sn: 0.06 to 0.6 wt%, Al: tr to 3 wt%, Mn: 0.1 A compacted sintered material containing ~ 3wt% and coated with Cu with the Fe particles covered with Cu of 90% or more is disclosed, and further, it is 10 ~ 150μm, and solids such as graphite and Pb with fine powder cut A sintered material added with 0.5 to 5 wt% of a lubricant is also disclosed.
This sintered material is strengthened by a large amount of Fe of 20 wt% or more, and has improved compatibility by coating Fe particles with Cu. Since this sintered material is an oil-impregnated bearing, a soft component such as Pb is not essential, emphasis is placed on strengthening and conformability, and the porosity is increased to 15 to 28 vol% for further oil impregnation. In addition, sizing is performed after sintering.

  Similarly, Patent Document 2 relating to sintered bearings discloses an oil-impregnated sintered bearing in which aluminum oxide or silicon nitride particles of preferably 50 μm or less are embedded in a bronze base material. The bearing is manufactured by so-called sizing through a mandrel after sintering.

In Patent Document 3, hard particles such as 10-40% Pb, 0.1-10% Sn, 10-30% Mo, Co, Fe ₃ P, FeB, Fe ₂ B, Ni, or Co-based self-fluxing alloys, the balance A sintered copper alloy comprising Cu is disclosed. Since this sintered copper alloy contains a large amount of Pb, corrosion is likely to occur under fluid lubrication conditions. Therefore, in the patent document 4, the Pb content is set to less than 10%, and the majority of hard particles are made of Cu. A sliding material dispersed in the grain, the grain boundary of Cu grain, and the boundary between Cu grain and Pb grain was proposed. The idea of this material design is that the lack of wear resistance due to the reduction of the Pb content is compensated by specifying the hard particle dispersion points.
Japanese Patent No. 2617334 Japanese Patent No.2697941 JP-A-57-50884 US Patent No. 5303617

  As stated at the beginning, the current copper alloy for bushings of A / T contained Pb, and Pb could not be completely eliminated. The above-mentioned Patent Document 4 focuses on corrosion under fluid lubrication conditions and does not consider seizure resistance under boundary lubrication conditions.

  In order to solve the above-mentioned problem, the present invention is made of a copper alloy containing no graphite but containing Pb, and 3% by area or more of graphite particles are exposed on the sliding surface, and particularly the surface roughness of the sliding surface. The present invention provides a copper alloy bushing for A / T that exhibits excellent performance when (Ra) is used at 1 μm or less.

In the present invention, it is preferable to contain hard particles. The hard particles are particles that are substantially harder than the copper alloy and enhance the wear resistance of the copper alloy. Specifically, hard particles are Fe ₂ P, Fe ₃ P, FeB, Fe ₂ B, Mo, Fe-Cr, Fe-Mn, Fe-Ni, Fe-Si, Fe-W, Fe-Mo, Fe-V , Fe-Ti, Fe-Nb, CuP, Cr, SiC, TiC, WC, B ₄ C, TiN, cubic BN, Si ₃ N ₄ , SiO ₂ , ZrO ₂ , Al ₂ O ₃ , Si-Mn, Cu -Si, FeS, Ni or Co-based self-fluxing alloys. Further preferred Fe particles are Fe ₃ P.
If the amount of hard particles is less than 1 wt%, the wear resistance is low, while if it exceeds 10 wt%, the wear of the counterpart material increases and the strength of the sintered material decreases.

  Conventionally, Pb has been indispensable for copper alloys used under boundary lubrication conditions such as A / T bushings. This is because the Pb phase exhibits self-lubricating properties under boundary lubrication conditions, but solid lubricants such as graphite do not have self-lubricating properties comparable to Pb. On the other hand, graphite has a self-lubricating property, but its conformability is poorer than that of Pb, so that the solid contact state continues. Need to be exposed. In the present invention, graphite particles exposed at 3% by area or more on the sliding surface prevent seizure under boundary lubrication conditions.

  In addition to the above components, the copper alloy of the present invention may contain, if necessary, 15% or less Sn, 5% or less Zn, 3% or less P, 3% or less Ni, 10% or less Fe, etc. One or more kinds may be contained, but Pb is not contained because it causes corrosion.

  The method for producing a sintered copper alloy according to the present invention can be produced by the two-stage sintering method described in Patent Document 4, column 4, lines 52 to 65. In use, it is necessary to scrape the surface to ensure a predetermined surface roughness and graphite exposed area.

When the surface roughness (Ra) is 1 μm or more, before the transition from the solid contact state to the fluid lubrication, the copper alloy is covered on the graphite and the self-lubricating property cannot be exhibited. When the surface roughness (Ra) is 1 μm or less, the copper alloy is not covered on the graphite, and the graphite is exposed on the sliding surface and can exhibit good lubricity, so that particularly good performance can be obtained.
Since the conventional Pb-containing sintered copper alloy has excellent compatibility with Pb, it is desirable in terms of seizure resistance to reduce the sliding surface roughness, but it is not essential. Pb can be contained in a large amount because Pb has a good bondability with a copper alloy. On the other hand, graphite has a poor bondability with a copper alloy and easily falls off, and if the content is excessively increased, the strength of the structure also decreases, so that it cannot be contained as much as Pb. In order to ensure seizure resistance equivalent to Pb in a small amount, it is necessary to control the exposure rate and preferably the surface roughness of graphite.
Hereinafter, the present invention will be described in detail by way of examples.

FIG. 1 is a graph showing the relationship between the graphite amount (wt%), particle size, and graphite exposure rate (area%) of a CuFe ₃ P-based sintered alloy. The surface of the sintered alloy was finished so that the roughness (Ra) was 1.0 μm.
Although the graphite exposure rate increases with the amount of graphite, the smaller the particle size, the smaller the graphite exposure rate even with the same amount of graphite.

  The difference in the graphite exposure rate occurs because the Cu alloy is stretched during the surface finishing and coats the graphite. If the graphite particle size is small, it is easy to coat, and if the particle size is large, everything is not coated, and the exposed part becomes large.

FIG. 2 is a graph showing the relationship between the graphite exposure rate and the seizure load.
The seizure load was measured by a 3-pin / disk test (peripheral speed: 3 m / s, lubrication method: ATF (T-4) 30 mg applied). The load application method was as shown in FIG.
It can be seen from FIG. 2 that the lower limit of seizure load is determined by the graphite exposure rate. From the above results, the graphite exposure rate was limited to 3% or more.

FIG. 4 is a graph showing the relationship between the surface roughness (Ra) of the CuFe ₃ P-based sintered alloy and the seizure load. The measuring method of the seizure load is the same as that described above. The surface roughness was set in the range of the horizontal axis in FIG. 4 by changing the amount of graphite and its particle size. FIG. 4 shows that the seizure load increases when the sliding surface roughness is 1 μm or less.

FIG. 5 is a graph showing the relationship between the graphite amount (wt%) and the surface roughness (Ra) of the sintered alloy mentioned with reference to FIG. This graph shows the following.
-The surface roughness (Ra) becomes rougher as the amount of graphite (wt%) and the particle size increase.
(b) When the graphite particles are as fine as 5 μm, the surface roughness (Ra) is almost constant regardless of the graphite amount (wt%). This is because fine graphite is difficult to drop out of the copper alloy, and the vacancies when dropped are small.

The surface roughness was measured on a flat plate whose surface was finished by the following method.
Testing machine: General-purpose lathe Test material: Sintered plate Chip: 0.8R
Feed: 0.105mm
Rotation speed: 500rpm
Track diameter: 12.5-32.5mm

  As described above, according to the present invention, a copper alloy having sufficient seizure resistance as an A / T bush can be obtained without adding Pb.

It is a graph which shows the relationship between a graphite exposure rate and a seizing load. It is a graph which shows the load application pattern in a seizure load measurement test. It is a graph which shows the relationship between a graphite amount and a graphite exposure rate. It is a graph which shows the relationship between a sliding surface roughness and a seizure load. It is a graph which shows the relationship between the amount of graphite and surface roughness. It is a microscope picture of the material of Table 1 and No. 1.

Claims (4)

A copper alloy bushing for an automatic transmission, which is made of a copper alloy not containing Pb and containing graphite, and 3% by area or more of graphite particles are exposed on the sliding surface. 2. A copper alloy bushing for an automatic transmission according to claim 1, wherein the bearing has good bearing characteristics when used with a surface roughness (Ra) of 1 [mu] m or less. The copper alloy bushing for an automatic transmission according to claim 1 or 2, wherein the copper alloy further contains 1 to 10 wt% of hard particles, and is sintered and laminated on a back metal. The copper alloy may further comprise one or two selected from the group consisting of 15% or less of Sn, 5% or less of Zn, 3% or less of P, 3% or less of Ni, and 10% or less of Fe, by weight. The copper alloy bushing for an automatic transmission according to any one of claims 1 to 3, characterized in that it contains more than one element.

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