Browse Publications Technical Papers 1999-01-3767
1999-11-15

Benefits of Profiling Tapered Roller Bearings - Matching Driveline Component Performance to the Demands of Higher Horsepower Engines of Heavy Duty Trucks 1999-01-3767

The heavy-duty trucking industry is continuing to move toward the use of higher horsepower engines. Engines exceeding 450 horsepower have become increasingly popular, with 500 - 600 horsepower engines expected to share a significant portion of the truck engine market in the next decade {Reference 1}. Sometimes these higher horsepower engines are used with existing gross combined vehicle weight, simply to increase the speed at which payloads are delivered. However, when higher engine horsepower is used to transport increased payloads, the result is higher loads and stresses on all driveline components between the engine and the wheels. All components downstream of the engine could be adversely affected.
The objectives of this paper are to:
  1. 1
    Alert truck axle and transmission manufacturers, as well as the trucking industry, of the potential effects of using higher horsepower engines in combination with increased payloads, with current/existing driveline components,
  2. 2
    Quantify the increase in internal contact stresses of tapered roller bearings used in typical truck drive line applications due to the combination of higher horsepower and increased gross combined vehicle weights,
  3. 3
    Describe the general methodology and factors considered in calculating these stresses, and
  4. 4
    Show that designing special internal profiles on tapered roller bearings can lower maximum contact stresses to acceptable levels.
In typical axle and transmission designs, high bearing contact stresses due to increased engine horsepower and payloads can be reduced, often to acceptable levels, using the same bearing envelope size, with special internal profiling. Consequently, redesign of shafts and housings to accommodate larger and heavier bearings may not be required. However, in some cases the stresses are so high that redesign can not be avoided. To illustrate these points, analyses of tapered roller bearings in typical tandem axles, single axles and transmissions will be used. The analyses show the maximum inner race roller-raceway contact stresses before and after profiling, as well as appropriate design and material limits. The loading for the examples is based on the Chicago to Portland (ChiPort) duty cycle, which is commonly used in application analysis.
The results presented in this paper have been generated analytically. Analytical tools developed by the Timken Corporation have accurately predicted satisfactory performance and acceptable stress values in existing applications. The same tools now predict higher stresses in these new applications having higher horsepower and increased payloads. This paper provides the means for communicating these concerns to the truck industry and serves as a reminder for driveline manufacturers to review loads and stresses if higher horsepower engines are being considered in conjunction with higher payloads.

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