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Development of the aluminum alloy bearing with higher wear resistance
JSAE Review 21 (2000) 321}325
Development of the aluminum alloy bearing with higher wear resistance Toru Desaki, Yasuaki Goto, Soji Kamiya Research Department, Taiho Kogyo Co., Ltd., 2-47, Hosoya-cho, Toyota-shi, Aichi 471-8502, Japan Received 8 November 1999; received in revised form 17 January 2000
Abstract The recent demands for higher performance and lower fuel consumption of automotive engines require the bearings to operate under severe conditions. As a result of these requirements, engine bearings are used under higher unit loads and higher temperatures, where the oil "lm thickness between bearing and shaft is increasingly thinner. One of the problems with conventional aluminum alloy bearings used under these conditions is the low wear resistance. For this reason, we have developed a new aluminum alloy bearing that allows a higher wear resistance. This paper describes the mechanism to upgrade the wear resistance and the performance of this new bearing material. 2000 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved.
1. Introduction Higher output and lower fuel consumption characterize the recent engines used for the automobiles, so that the viscosity of the engine oil has decreased and the unit load on the crankshaft and connecting-rod bearings has increased. As a result the oil "lm thickness between bearings and shaft has become increasingly thinner and the operating conditions of the bearings have become more severe. When bearings are used under thinner oil "lm conditions, the bearings and shaft can easily contact directly, and there is the danger that excessive wear of bearing and seizure are caused. The conventional bearing materials are copper lead alloy with lead base overlay and aluminum alloy. Corrosion resistance and wear resistance of copper lead alloy bearings with lead base overlay are inferior to those of aluminum alloy bearings. In addition, lead is an environmentally toxic material. Therefore, demands for aluminum alloy bearings with improved bearing performance are expected. The requirements for cost reduction of the engine have also increased, and one of the cost reduction items to be examined is the acceptance of a cast iron shaft, which has a lower cost than a forged steel shaft. In general, with nodular graphite cast iron used in a cast iron shaft, can easily form barr, caused by the ferrite which exists around the graphite. Metal-to-metal
contact often happens with the barr, and there are many other causes that increase the wear of the bearing [1]. Thus it is di$cult to apply copper lead alloy with lead base overlay in such a case. The alloy of Al}Sn}Si with dispersed Si as a hard particle is generally used for an aluminum alloy bearing. Wear resistance and seizure resistance improve due to the lapping action of the shaft surface and the removal of adhesion by the Si particle [2,3]. However, the e!ect of Si is insu$cient under severe conditions and improvement of the wear resistance is needed. For these reasons, we attempted to improve the wear resistance and seizure resistance by controlling the Si particle size contained in the aluminum alloy and the hardness of the bearing alloy. Its fatigue resistance is almost the same as the conventional material. This paper details the mechanism of the wear resistance improvement of this bearing material and the bearing performance.
2. The e4ect of Si particle size and hardness of the alloy on wear resistance [4] Wear tests were conducted to clarify the in#uence of Si particle size and hardness of the alloy against wear resistance. The evaluations were carried out using the static load wear tester shown in Fig. 1, and under the conditions
0389-4304/00/$ 20.00 2000 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved. PII: S 0 3 8 9 - 4 3 0 4 ( 0 0 ) 0 0 0 5 1 - 5
JSAE20004141
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T. Desaki et al. / JSAE Review 21 (2000) 321}325
Fig. 2. Relationship between Si particle size and wear depth. Fig. 1. Schematic of wear tester under static load.
Table 1 Test conditions Static load
490 N
Test pattern & cycles Oil temp. Shaft Material Roughness Hardness
Go}Stop (0}1000 rpm) 50 000 cycles 1203C Quenched steel 0.9}1.1 lm Rz 720}850 HV1 Fig. 3. Relationship between hardness of alloy and wear depth.
shown in Table 1. The test program is a cyclic pattern of the start-stop operation which often causes bearing wear. The test duration was 50 000 cycles. The test bearing is an Al}Sn}Si alloy with back-steel which has a cylindrical form. Si particle size was adjusted to the range from 2.5 to 5.5 lm in the mean of the circular equivalent diameter. Hardness of the alloy was adjusted to 40}55 HV. The amount of wear was determined by the changes of the wear depth measured by the circularity of the bearing inner diameter before and after tests. The relationship between the wear depth and Si particle size is shown in Fig. 2. When Si particle size was larger, the wear depth decreased, and there was almost no di!erence of wear depth above 4.0 lm of Si particle size. The in#uence of hardness of the bearing alloy is shown in Fig. 3. When Si particle size was 2.5 lm, there was little in#uence of hardness of the alloy on the bearing wear. In the case of 4.0 lm, wear depth decreased with greater hardness of the alloy.
3. The mechanism of the wear resistance improvement To study why the wear resistance is improved when Si particle size is large and hardness of the alloy is high, observations of the sliding surface and the cross-section of the bearing after wear tests were performed using
Fig. 4. Cross-sectional structure after 50 000 cycles.
a scanning electron microscope and an optical microscope. The observation results in cross-section are shown in Fig. 4. The concentration of Si on the sliding surface seen in these photographs was observed in all test specimens. Areas where Si fell from the sliding surface were observed when Si particle size was small or when hardness of the alloy was low. These phenomena were observed in the surface observation as well. Secondly, the test results showing the relationship of wear depth and Si content of the sliding surface to number of cycles are shown in Fig. 5. Hardness of the test bearings was 53 HV. When Si particle size is 2.5 lm, wear depth increases with number of cycles. Si content of the
T. Desaki et al. / JSAE Review 21 (2000) 321}325
323
Fig. 6. Schematic of alternating load bearing tester and test conditions.
Fig. 5. Changes of Si content of sliding surface and wear depth with number of cycles.
surface increased rapidly in the initial stage, and after that it hardly changed. However, when Si particle size was 4.0 lm, both wear depth and Si content of the surface increased gradually with the number of cycles. From these results, the mechanism of the wear resistance improvement was estimated as follows. As wear progresses, only the comparatively soft aluminum alloy matrix wears, and consequently the concentration of Si occurs on the sliding surface. When Si content of the sliding surface increases, the load resulting from Si particles increases too. As a result, wear depth of the bearing is decreased. When Si particle size is small or when hardness of the alloy is low, both the concentration of Si by aluminum alloy matrix wear and falling o! of Si particles occur simultaneously. Therefore, wear progresses without changing Si content of the surface. However, when Si particle size is large and hardness of the alloy is high, wear does not progress easily because Si particles are strongly held in the alloy and Si particles are prevented from falling o! the sliding surface.
4. Development of the new bearing material Based on the above results, development of the new aluminum alloy bearing with improved wear resistance was investigated. The mechanical properties of the new bearing material were examined together with chemical composition of the alloy to improve the performance such as fatigue, seizure and wear resistance. 4.1. Fatigue resistance Si particle size 5.5 lm and hardness 53 HV material which showed excellent results in the wear test were selected for the trial material as the new bearing, and its fatigue resistances was con"rmed. Chemical composition
Fig. 7. Results of the fatigue test under alternating load.
is the same as the conventional aluminum alloy bearing (Al}12Sn}2.7Si}1.5Pb}1Cu}0.2Cr). First, the fatigue resistance of the trial material was tested under the alternating load. The alternating load bearing tester used for this test and the test conditions are shown in Fig. 6. Fatigue occurrence was detected from the rise in the bearing back-side temperature due to the fatigue crack occurrence, and fatigue life was de"ned at the operation time until the fatigue crack occurred [5]. The results of the fatigue test are shown in Fig. 7. Fatigue resistance of the trial material was inferior to the conventional material, and its fatigue life was about half. The reason why fatigue resistance was inferior to the conventional bearing was thought to be the in#uence of the Sn structure which was coarsened by heat treatment given to enlarge Si particle size. Coarse Sn phase easily becomes the initiating point of fatigue crack occurrence and the cracks are easily propagated along the Sn phase. Therefore, the new alloy was improved to upgrade fatigue resistance. Sn content is reduced by about , and Sn structure is made "ner than the conventional material. By not adding Pb, the Sn}Pb eutectic reaction is removed, and melting point of Sn phase is raised from 1833C to 2323C, thus preventing the decline of tensile strength of the alloy at high temperature. This also removes the toxic Pb which a!ects the environment. Moreover, through the examination of the kind of strengthening matrix and its quantity to raise fatigue strength of the alloy, we developed the new material which has the chemical composition shown in
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Table 2 Chemical composition of developed alloy
Developed Conventional
Al
Sn
Si
Pb
Cu
Cr
Zr
Bal. Bal.
4.5 12.5
2.7 2.7
* 1.8
1.5 1
0.2 0.2
0.15 *
Table 3 Mechanical properties of developed alloy
Developed Conventional
Fig. 9. Schematic of Rotating load bearing tester and test conditions.
TS (MPa)
EL (%)
Hardness (HV)
170 142
24 25
53 50
Fig. 10. Results of the fatigue test under rotating load. Fig. 8. Results of the fatigue test under alternating load.
Table 2 and the mechanical properties shown in Table 3. Si particle size and hardness of the alloy are 5.5 lm and 53 HV. The results of the fatigue test with the developed material using the above alternating load bearing tester are shown in Fig. 8. In spite of large Si particle size, the developed material showed good fatigue resistance which was almost equal to the conventional material due to the e!ect of the structure improvement and the fatigue strength improvement. Presuming the rotating load in the engine by the inertia force, fatigue tests under the rotating load were conducted using the rotating load bearing tester and the test conditions shown in Fig. 9. The results of the fatigue test under rotating load are shown in Fig. 10. The developed material showed excellent fatigue resistance under the rotating load and it was about 10 times longer in the fatigue life compared with the conventional material. 4.2. Seizure resistance It has already been reported that the removal action of the adhesion on the shaft become stronger with enlarged Si particle size, and seizure resistance also improves [6]. Seizure resistance of the developed material was also con"rmed.
Fig. 11. Results of the seizure test under static load.
The results of the seizure test are shown in Fig. 11. Inspite of lower Sn content and higher strength of the alloy, the developed material showed excellent seizure resistance, about two times higher in comparison with the conventional material for seizure load. 4.3. Wear resistance The wear resistance of the developed material was con"rmed using the static load wear tester described before. The results of the wear test are shown in Fig. 12. The developed material indicated good wear resistance and wear depth was about that of the conventional material. Finally the wear tests with the cast iron shaft were conducted using the wear tester shown in Fig. 13, which is the presumed cause of local contact.
T. Desaki et al. / JSAE Review 21 (2000) 321}325
Fig. 12. Results of the wear test under static load.
325
Fig. 14. Results of the wear test.
could achieve almost equal fatigue resistance under the alternating load and superior fatigue resistance under the rotating load compared with conventional material. Seizure resistance of the developed bearing indicated good results.
Fig. 13. Schematic of wear tester with local contact and test conditions.
The results are shown in Fig. 14. Wear resistance with the cast iron shaft was superior to the conventional bearing, and the developed material showed about three times better wear resistance.
5. Summary (1) The developed material with average Si particle size adjusted to 5.5 lm and alloy hardness to 53 HV indicates 3}4 times better wear resistance compared with the conventional material. (2) It is thought that the mechanism of the wear resistance improvement is that the load is resisted by the concentrated Si on the sliding surface that is held strongly by su$cient hardness of the matrix. (3) Even with average Si particle size of 5.5 lm, reconsidering the structure and the strength of the alloy, it
This new developed aluminum bearing material which is free from toxic Pb has the possibility to be adopted for the engine in which higher wear resistance is required. References [1] Soda, N. et al., Wear of metals against the surface with cavities with special reference to that of bearing metals against FCD shaft (in Japanese with English summary), J. JSLE, Vol. 24, No. 9, pp. 611}618 (1979). [2] Fukuoka, T. et al., Study on aluminum alloy bearings containing hard particle (in Japanese with English summary), Trans. JSME, Vol. 53, No. 490, pp. 1232}1236 (1987. 6). [3] Fukuoka, T. et al., E!ects of hardness of particulate inclusions dispersed in aluminum alloy bearings (in Japanese with English summary), Trans. JSME, Vol. 53, No. 490, pp. 1237}1242 (1987. 6). [4] Goto, Y. et al., Aluminum alloy bearing with higher wear resistance (in Japanese), Proceedings of JAST Tribology Conference, Nagoya, No. 1E18, p. 257 (1998. 11). [5] Fukuoka, T. et al., Fatigue and life of plain bearings under alternating and rotating loads, Proceedings of JSLE International Tribiology Conference, Tokyo, Vol. I p. 91 (1985. 7). [6] Fukuoka, T. et al., E!ects of hard particles added to aluminum alloy bearings (in Japanese with English summary), Transactions of JSME, Vol. 53, No. 490, pp. 1242}1248 (1987. 6).
Development of the aluminum alloy bearing with higher wear resistance Toru Desaki, Yasuaki Goto, Soji Kamiya Research Department, Taiho Kogyo Co., Ltd., 2-47, Hosoya-cho, Toyota-shi, Aichi 471-8502, Japan Received 8 November 1999; received in revised form 17 January 2000
Abstract The recent demands for higher performance and lower fuel consumption of automotive engines require the bearings to operate under severe conditions. As a result of these requirements, engine bearings are used under higher unit loads and higher temperatures, where the oil "lm thickness between bearing and shaft is increasingly thinner. One of the problems with conventional aluminum alloy bearings used under these conditions is the low wear resistance. For this reason, we have developed a new aluminum alloy bearing that allows a higher wear resistance. This paper describes the mechanism to upgrade the wear resistance and the performance of this new bearing material. 2000 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved.
1. Introduction Higher output and lower fuel consumption characterize the recent engines used for the automobiles, so that the viscosity of the engine oil has decreased and the unit load on the crankshaft and connecting-rod bearings has increased. As a result the oil "lm thickness between bearings and shaft has become increasingly thinner and the operating conditions of the bearings have become more severe. When bearings are used under thinner oil "lm conditions, the bearings and shaft can easily contact directly, and there is the danger that excessive wear of bearing and seizure are caused. The conventional bearing materials are copper lead alloy with lead base overlay and aluminum alloy. Corrosion resistance and wear resistance of copper lead alloy bearings with lead base overlay are inferior to those of aluminum alloy bearings. In addition, lead is an environmentally toxic material. Therefore, demands for aluminum alloy bearings with improved bearing performance are expected. The requirements for cost reduction of the engine have also increased, and one of the cost reduction items to be examined is the acceptance of a cast iron shaft, which has a lower cost than a forged steel shaft. In general, with nodular graphite cast iron used in a cast iron shaft, can easily form barr, caused by the ferrite which exists around the graphite. Metal-to-metal
contact often happens with the barr, and there are many other causes that increase the wear of the bearing [1]. Thus it is di$cult to apply copper lead alloy with lead base overlay in such a case. The alloy of Al}Sn}Si with dispersed Si as a hard particle is generally used for an aluminum alloy bearing. Wear resistance and seizure resistance improve due to the lapping action of the shaft surface and the removal of adhesion by the Si particle [2,3]. However, the e!ect of Si is insu$cient under severe conditions and improvement of the wear resistance is needed. For these reasons, we attempted to improve the wear resistance and seizure resistance by controlling the Si particle size contained in the aluminum alloy and the hardness of the bearing alloy. Its fatigue resistance is almost the same as the conventional material. This paper details the mechanism of the wear resistance improvement of this bearing material and the bearing performance.
2. The e4ect of Si particle size and hardness of the alloy on wear resistance [4] Wear tests were conducted to clarify the in#uence of Si particle size and hardness of the alloy against wear resistance. The evaluations were carried out using the static load wear tester shown in Fig. 1, and under the conditions
0389-4304/00/$ 20.00 2000 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved. PII: S 0 3 8 9 - 4 3 0 4 ( 0 0 ) 0 0 0 5 1 - 5
JSAE20004141
322
T. Desaki et al. / JSAE Review 21 (2000) 321}325
Fig. 2. Relationship between Si particle size and wear depth. Fig. 1. Schematic of wear tester under static load.
Table 1 Test conditions Static load
490 N
Test pattern & cycles Oil temp. Shaft Material Roughness Hardness
Go}Stop (0}1000 rpm) 50 000 cycles 1203C Quenched steel 0.9}1.1 lm Rz 720}850 HV1 Fig. 3. Relationship between hardness of alloy and wear depth.
shown in Table 1. The test program is a cyclic pattern of the start-stop operation which often causes bearing wear. The test duration was 50 000 cycles. The test bearing is an Al}Sn}Si alloy with back-steel which has a cylindrical form. Si particle size was adjusted to the range from 2.5 to 5.5 lm in the mean of the circular equivalent diameter. Hardness of the alloy was adjusted to 40}55 HV. The amount of wear was determined by the changes of the wear depth measured by the circularity of the bearing inner diameter before and after tests. The relationship between the wear depth and Si particle size is shown in Fig. 2. When Si particle size was larger, the wear depth decreased, and there was almost no di!erence of wear depth above 4.0 lm of Si particle size. The in#uence of hardness of the bearing alloy is shown in Fig. 3. When Si particle size was 2.5 lm, there was little in#uence of hardness of the alloy on the bearing wear. In the case of 4.0 lm, wear depth decreased with greater hardness of the alloy.
3. The mechanism of the wear resistance improvement To study why the wear resistance is improved when Si particle size is large and hardness of the alloy is high, observations of the sliding surface and the cross-section of the bearing after wear tests were performed using
Fig. 4. Cross-sectional structure after 50 000 cycles.
a scanning electron microscope and an optical microscope. The observation results in cross-section are shown in Fig. 4. The concentration of Si on the sliding surface seen in these photographs was observed in all test specimens. Areas where Si fell from the sliding surface were observed when Si particle size was small or when hardness of the alloy was low. These phenomena were observed in the surface observation as well. Secondly, the test results showing the relationship of wear depth and Si content of the sliding surface to number of cycles are shown in Fig. 5. Hardness of the test bearings was 53 HV. When Si particle size is 2.5 lm, wear depth increases with number of cycles. Si content of the
T. Desaki et al. / JSAE Review 21 (2000) 321}325
323
Fig. 6. Schematic of alternating load bearing tester and test conditions.
Fig. 5. Changes of Si content of sliding surface and wear depth with number of cycles.
surface increased rapidly in the initial stage, and after that it hardly changed. However, when Si particle size was 4.0 lm, both wear depth and Si content of the surface increased gradually with the number of cycles. From these results, the mechanism of the wear resistance improvement was estimated as follows. As wear progresses, only the comparatively soft aluminum alloy matrix wears, and consequently the concentration of Si occurs on the sliding surface. When Si content of the sliding surface increases, the load resulting from Si particles increases too. As a result, wear depth of the bearing is decreased. When Si particle size is small or when hardness of the alloy is low, both the concentration of Si by aluminum alloy matrix wear and falling o! of Si particles occur simultaneously. Therefore, wear progresses without changing Si content of the surface. However, when Si particle size is large and hardness of the alloy is high, wear does not progress easily because Si particles are strongly held in the alloy and Si particles are prevented from falling o! the sliding surface.
4. Development of the new bearing material Based on the above results, development of the new aluminum alloy bearing with improved wear resistance was investigated. The mechanical properties of the new bearing material were examined together with chemical composition of the alloy to improve the performance such as fatigue, seizure and wear resistance. 4.1. Fatigue resistance Si particle size 5.5 lm and hardness 53 HV material which showed excellent results in the wear test were selected for the trial material as the new bearing, and its fatigue resistances was con"rmed. Chemical composition
Fig. 7. Results of the fatigue test under alternating load.
is the same as the conventional aluminum alloy bearing (Al}12Sn}2.7Si}1.5Pb}1Cu}0.2Cr). First, the fatigue resistance of the trial material was tested under the alternating load. The alternating load bearing tester used for this test and the test conditions are shown in Fig. 6. Fatigue occurrence was detected from the rise in the bearing back-side temperature due to the fatigue crack occurrence, and fatigue life was de"ned at the operation time until the fatigue crack occurred [5]. The results of the fatigue test are shown in Fig. 7. Fatigue resistance of the trial material was inferior to the conventional material, and its fatigue life was about half. The reason why fatigue resistance was inferior to the conventional bearing was thought to be the in#uence of the Sn structure which was coarsened by heat treatment given to enlarge Si particle size. Coarse Sn phase easily becomes the initiating point of fatigue crack occurrence and the cracks are easily propagated along the Sn phase. Therefore, the new alloy was improved to upgrade fatigue resistance. Sn content is reduced by about , and Sn structure is made "ner than the conventional material. By not adding Pb, the Sn}Pb eutectic reaction is removed, and melting point of Sn phase is raised from 1833C to 2323C, thus preventing the decline of tensile strength of the alloy at high temperature. This also removes the toxic Pb which a!ects the environment. Moreover, through the examination of the kind of strengthening matrix and its quantity to raise fatigue strength of the alloy, we developed the new material which has the chemical composition shown in
324
T. Desaki et al. / JSAE Review 21 (2000) 321}325
Table 2 Chemical composition of developed alloy
Developed Conventional
Al
Sn
Si
Pb
Cu
Cr
Zr
Bal. Bal.
4.5 12.5
2.7 2.7
* 1.8
1.5 1
0.2 0.2
0.15 *
Table 3 Mechanical properties of developed alloy
Developed Conventional
Fig. 9. Schematic of Rotating load bearing tester and test conditions.
TS (MPa)
EL (%)
Hardness (HV)
170 142
24 25
53 50
Fig. 10. Results of the fatigue test under rotating load. Fig. 8. Results of the fatigue test under alternating load.
Table 2 and the mechanical properties shown in Table 3. Si particle size and hardness of the alloy are 5.5 lm and 53 HV. The results of the fatigue test with the developed material using the above alternating load bearing tester are shown in Fig. 8. In spite of large Si particle size, the developed material showed good fatigue resistance which was almost equal to the conventional material due to the e!ect of the structure improvement and the fatigue strength improvement. Presuming the rotating load in the engine by the inertia force, fatigue tests under the rotating load were conducted using the rotating load bearing tester and the test conditions shown in Fig. 9. The results of the fatigue test under rotating load are shown in Fig. 10. The developed material showed excellent fatigue resistance under the rotating load and it was about 10 times longer in the fatigue life compared with the conventional material. 4.2. Seizure resistance It has already been reported that the removal action of the adhesion on the shaft become stronger with enlarged Si particle size, and seizure resistance also improves [6]. Seizure resistance of the developed material was also con"rmed.
Fig. 11. Results of the seizure test under static load.
The results of the seizure test are shown in Fig. 11. Inspite of lower Sn content and higher strength of the alloy, the developed material showed excellent seizure resistance, about two times higher in comparison with the conventional material for seizure load. 4.3. Wear resistance The wear resistance of the developed material was con"rmed using the static load wear tester described before. The results of the wear test are shown in Fig. 12. The developed material indicated good wear resistance and wear depth was about that of the conventional material. Finally the wear tests with the cast iron shaft were conducted using the wear tester shown in Fig. 13, which is the presumed cause of local contact.
T. Desaki et al. / JSAE Review 21 (2000) 321}325
Fig. 12. Results of the wear test under static load.
325
Fig. 14. Results of the wear test.
could achieve almost equal fatigue resistance under the alternating load and superior fatigue resistance under the rotating load compared with conventional material. Seizure resistance of the developed bearing indicated good results.
Fig. 13. Schematic of wear tester with local contact and test conditions.
The results are shown in Fig. 14. Wear resistance with the cast iron shaft was superior to the conventional bearing, and the developed material showed about three times better wear resistance.
5. Summary (1) The developed material with average Si particle size adjusted to 5.5 lm and alloy hardness to 53 HV indicates 3}4 times better wear resistance compared with the conventional material. (2) It is thought that the mechanism of the wear resistance improvement is that the load is resisted by the concentrated Si on the sliding surface that is held strongly by su$cient hardness of the matrix. (3) Even with average Si particle size of 5.5 lm, reconsidering the structure and the strength of the alloy, it
This new developed aluminum bearing material which is free from toxic Pb has the possibility to be adopted for the engine in which higher wear resistance is required. References [1] Soda, N. et al., Wear of metals against the surface with cavities with special reference to that of bearing metals against FCD shaft (in Japanese with English summary), J. JSLE, Vol. 24, No. 9, pp. 611}618 (1979). [2] Fukuoka, T. et al., Study on aluminum alloy bearings containing hard particle (in Japanese with English summary), Trans. JSME, Vol. 53, No. 490, pp. 1232}1236 (1987. 6). [3] Fukuoka, T. et al., E!ects of hardness of particulate inclusions dispersed in aluminum alloy bearings (in Japanese with English summary), Trans. JSME, Vol. 53, No. 490, pp. 1237}1242 (1987. 6). [4] Goto, Y. et al., Aluminum alloy bearing with higher wear resistance (in Japanese), Proceedings of JAST Tribology Conference, Nagoya, No. 1E18, p. 257 (1998. 11). [5] Fukuoka, T. et al., Fatigue and life of plain bearings under alternating and rotating loads, Proceedings of JSLE International Tribiology Conference, Tokyo, Vol. I p. 91 (1985. 7). [6] Fukuoka, T. et al., E!ects of hard particles added to aluminum alloy bearings (in Japanese with English summary), Transactions of JSME, Vol. 53, No. 490, pp. 1242}1248 (1987. 6).