Most durable and consumable goods in the United States are transported by over-the-road trucking. On-time delivery depends on a durable, reliable power transmission system. In a heavy-duty, over-the-road environment, it’s not uncommon for these transmission systems to operate for more than 1 million miles without requiring repair. Discuss Cylindrical Roller Bearing needs.
Power Transmission Gearbox
A power transmission gearbox is composed of an input shaft, counter shafts, a main shaft and an output shaft. The input shaft transmits power through a system of gears driven by a motor, supported by a bearing mounted within the casing of the gearbox. This shaft transmits power to the counter shaft(s).
A gearbox may have only one counter shaft, but it typically it has two or three, spaced at equidistant positions in relation to the main shaft. Multiple counter shafts reduce loading on support bearings and gear sets but can increase heat and result in a loss of torque. Input and counter shaft support bearings (shown above) are cylindrical roller bearings. The gears of the counter shaft engage the gears on the main shaft to transmit power to the output shaft.
The main shaft is piloted into the end of the input shaft but turns independently. The main shaft is typically splined directly to the output shaft and supported by a pilot bearing at one end and a bearing mounted in the casing of the gearbox at the other.
Bearing Life Analysis
The example above shows a life analysis for the support bearings in a typical power transmission system. In such an analysis, the customer submits a bearing life goal, which in this case is 4,800 hours, representing 10 years or 1.2 million miles of service.
Gearbox life and reliability are calculated based on a given load and speed in a duty cycle of conditions, along with lubrication, contamination (if available) and shaft sloping at the bearing seats.
The reliability of a gearbox life is the probability the bearing will survive the required life. In this example, the bearings in the gearbox have a 97% chance of survival to the 4,800-hour goal, with an L10 life estimate of 14,291 hours.
Determing Bearing Lifespan
At Regal Rexnord™, we’ve developed power transmission analysis software to determine the lifespan and effectiveness of cylindrical, ball and spherical roller bearings. We can analyze the quasi-dynamic load and stress distributions within a bearing given externally applied loads -- including radial, axial and moment loads -- as we consider the effects of centrifugal roller loading.
Our software also calculates component stress, considering the effects of raceway profiling stress concentration. In addition to load and stress, the effects of lubrication and temperature are calculated from given technical specifications, type of lubrication and boundary temperatures.
Using the Regal Rexnord power transmission analysis with duty cycle gearbox life and reliability calculation techniques, we can select and optimize the proper bearing type to maximize the support bearing’s life potential for your gearbox, keeping your trucks on the road.
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Marlon Casey
Marlon Casey is an Engineering Manager with the Rexnord Bearing Group. He has spent 11 years with Link-Belt and over 31 years with Rexnord managing the Research & Development, Testing, Engineering Analysis, Product Design & Development and Product Engineering activities. Marlon’s responsibilities include conceptualizing, developing, maintaining, and improving bearing products required to support MB, Link-Belt, REX and Filament Industrial Bearing products. His skillsets and vast experience are regularly utilized by the manufacturing, commercial, and applications’ departments to provide an expert level of product knowledge to support customer needs.