Eco-friendly Product Development at SNR Roulements - NTN

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Eco-friendly Product Development at SNR Roulements Fig. 2 shows shapes of a conventional design and the new optimized design. The new hub design features a unique flange shape, each of its bolt-down segments being reinforced with two ribs. With this design, the mass of outer ring has been reduced by 20% and that of entire H/B by 15%. This weight reduction will mean a maximum weight reduction of 1,300 g per automobile axle. 20% weight reduction Fig. 2 Conventional design (left) and new optimized design (right) 2.2 Water pump bearing for automobile Fig. 4 shows an appearance of a conventional water pump for cooling an automotive engine, and Fig. 5 schematically illustrates the structure of the water pump. Many present-day water pumps used for cooling modern automotive engines incorporate integral shaft bearings that have a raceway surface on their shafts with their inner ring deleted. With a conventional structure in Fig. 5, the belt tension poses an offset load onto the bearing and causes the contact pressure to be greater. This problem in turn poses a challenge in providing longer life for the bearing. At the same time, resultant misalignment of the bearing relative to the shaft can cause water to pass the seal and enter the bearing. Consequently, the grease can leak out of the bearing, leading to poor lubrication of the bearing. The bearing can then develop abnormal noise and/or exhibit excessively short life. 2.1.2 Performance of new optimized design As described above, the new optimized design boasts a much reduced weight, while its rigidity is equivalent to that of conventional designs. Furthermore, because the bolt-down segments are reinforced with ribs, the stress occurring at the flange base of the new design is 35% smaller as shown in Fig. 3. Pulley Drain hole Seal Pump rotor 35% reduction in stress Drive shaft Stress Hub (pulley sheet) Pump body Fig. 4 View of Water pump Conventional design New optimized design Load from belt Fig. 3 Stress analysis results Integral shaft bearing Fig. 5 Water pump structure -35-
NTN TECHNICAL REVIEW No.772009 2.2.1 Structure of new bearing In order to achieve lower running noise, lighter weight and longer bearing life, we have developed a novel external bearing that has a shaft integrated with a flange. Fig. 6 shows a view of this novel external bearing, and Fig. 7 schematically illustrates the structure of this bearing. This structure ensures that the tension from the drive belt acts on the center of bearing, helping prevent misalignment of the bearing relative to the shaft. Compared with conventional designs, the contact pressure between the balls and raceway surface on this bearing is lower, leading to improved bearing durability. In addition, because our new bearing is free from bearing-shaft misalignment which will develop moment load, the balls will roll at the bottom of groove, resulting in lower running noise occurrence. Through improvement in our production technology, we have integrated the bearing and flange with the shaft, thereby we have successfully achieved an increase in load carrying capacity of bearing, increase in pump capacity, longer bearing life, lower noise emission and lighter weight. Fig. 8 summarizes changes in appearance and weight of water pump bearing over several years. 2.2.2 Determination of contact pressure occurring between balls and raceway surface So that a water pump on an automobile remains operative without any need for repair until the automobile reaches the end of its useful service life, the life of water pump bearing needs to satisfy 310 5 Flange Load from belt Shaft External bearing Fig. 6 View of external bearing Fig. 7 Structure of external bearing Greater pump capacity Longer life Weight reduction Drive belt for auxiliaries is directly engaged with the outer ring; this arrangement helps realize a space-saving pump design. Use of larger balls helps reduce contact pressure, mitigating adverse effect of press-fitting operation. 21% Optimization of water pump 571g Improvements • Greater load carrying capacity with bearing • Pump capacity • Bearing life • Noise level • Weight 451g 2004 2008 Years Fig. 8 Process of water pump bearing -36-
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Eco-friendly Product Development at SNR Roulements - NTN

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