Eco-friendly Product Development at SNR Roulements - NTN

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Eco-friendly Product Development at SNR Roulements 3.3 Low torque tapered roller bearings Tapered roller bearings are often used as transmission bearings because they can carry a greater combined axial and radial load compared with other bearing types of similar size. However, reduction in frictional torque occurring on this bearing type poses a challenge. The SNR tapered roller bearings for automotive transmissions boasts decreased frictional torque through adoption of NTN’s design and production technologies for low torque tapered roller bearings. The advantages of these SNR products can be defined as follows: (1) Special heat treatment process helps improve fatigue strength and resistance against dent mark that can result from foreign matter in lubricant. (2) Adoption of polyamide cage in which shear friction with oil is lower, compared with that in standard steel sheet cages (3) Improved design for bearing interior in order to improve load carrying capacity and rigidity and mitigate misalignment and frictional torque (optimized number and size of rollers, and special crowning on raceway surface and rolling surface) (4) Optimization of contact locations between inner ring flange surface, rollers, and raceway surface (5) Reduction in surface roughness of inner ring flange surface and roller end faces to reduce frictional torque on roller end faces Fig. 16 graphically plots information about comparisons of SNR's tapered roller bearing for transmission and a competitor’s tapered roller bearing, wherein the running speeds data of these bearings are plotted along the horizontal axis. As can be understood from this diagram, the bearing products of SNR boast 25 to 50% reduction in torque loss, compared with competitor’s products. 25% reduction in torque loss with transmission bearings means 2 g/km reduction in CO2 emissions per vehicle. In addition, use of low torque tapered roller bearings helps improve seizure resistance as well as quality of shift-change operation. 3.4 Automotive hub bearings About 50% of frictional torque occurring on a wheel bearing results from sliding friction on contact surface of seal(s). Therefore, the use of hub bearings featuring reduced sliding resistance is effective in reducing the CO2 emissions from the vehicle that incorporates low friction wheel bearings. However, reduced frictional resistance on a given seal often means jeopardized sealing performance of that seal. Therefore, there has been a challenge of meeting conflicting needs for reduced frictional resistance and improved sealing performance. SNR has developed a unique tribological effectcapable seal that boasts approx. 11% reduction in sliding resistance and 22% improvement in sealing performance, by improving lubrication quality on the sliding surface of seal lip. As SNR has applied the above-mentioned development concept to its currently present seal products, cost reduction and reduced development lead time have been achieved. 3.4.1 Advantages of tribological effect-capable seal products On our newly developed tribological effect-capable seals, the lip sliding surface of the slinger is uniquely shaped so that oil film is readily formed on it. 1.0 Running torque Nm 0.8 0.6 0.4 Competitor’s tapered roller bearing 0.2 SNR low torque tapered roller bearing 0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Running speed min -1 Fig. 16 Torque measurements with rotations -39-
NTN TECHNICAL REVIEW No.772009 Consequently, lower torque and mitigation of heat buildup have been achieved. Fig. 17 illustrates a cross-sectional plan of our seal, and a view of the contact area of the slinger. Micro-pores present in this contact area help form an oil film between the seal lip and slinger, and the oil film reduces friction on the seal lip. Furthermore, these micro-pores prevent wear caused by ingress and trapping of foreign matters. 3.4.2 Performance of tribological effect-capable seal Figs. 18 and 19 show running torque and test results of a muddy water bearing life test with conventional seal and our newly developed tribological effect-capable seal. Owing to reduced resistance on seal, the running torque has decreased by 11%, and the muddy water bearing life has increased by 22%. Enlarged view of contact area on slinger Micro-pores 3.5 Automotive suspension bearings To be able to operate without problems under severe operating conditions (environments such as muddy water), a sealed strut bearing needs to feature improved reliability and sealing performance. In challenging this issue, SNR has developed a unique low torque sealed strut bearing complete with a floating seal in order to satisfy requirements for both an improvement in running torque and sealing performance (Fig. 21). 3.5.1 Features of sealed strut bearings Muddy water resistance of a bearing is governed by lip performance of its seal. Therefore, it is important to develop a seal that is capable of satisfying both better sealing performance and stabler running torque performance. To address this challenge, we have recently developed a novel low torque sealed strut bearing complete with a floating seal. Fig. 20 shows a conventional design, and Fig. 21 illustrates our new design. For comparison purpose, Fig. 22 shows a structure of a different design, that is, an overmolded lip seal. Fig. 17 Seal shape on the slinger Torque Nm 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Conventional design Tribological effect-capable seal 11% reduction in running torque Seal area Bearing area Fig. 20 Usual design Fig. 18 Comparison of rotational friction between development seal and current one Muddy water bearing life h 700 600 500 400 300 200 100 0 Conventional design Tribological effect-capable seal 22% Fig. 19 Comparison of muddy water resistance between development seal and current one Fig. 21 SNR design: floating seal Fig. 22 Competitor design: overmolded lip seal -40-
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Eco-friendly Product Development at SNR Roulements - NTN

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