A new software tool called BCG-MinWeight has been developed by BCGear & Engineering, Inc., a provider of design and manufacturing engineering services for the gear industry, located in Detroit, Michigan. BCG-MinWeight specifies basic parameters for gear designs in order to optimize for size and weight. By providing inputs for design ratio, power, and input RPM along with contact and bending stress parameters, a set of design outputs can be generated that specify center distances, face widths, normal diametral pitches, pitch diameters, and numbers of teeth.
Additional controlling factors that are used in the BCG-MinWeight optimization process include pitch-line velocity, face width to pitch diameter ratio, web thickness, housing weight, planetary carrier weight, and others. Additional outputs from the optimization process include estimates for actual contact and bending stresses, pitch line velocities, load distribution factors, dynamic factors, and AGMA quality levels.
The primary goal of the BCG-MinWeight software application is to maximize the fidelity of initial designs so that size and weight estimates can be accurately defined before the centerlines are established and the gear ratios are locked down. It’s relatively easy to change design parameters such as pressure angles or face widths during the development process, but it’s much more difficult to change reduction ratios and center distances after the preliminary design concept has been approved.
Another reason for using BCG-MinWeight is to establish optimal ratio splits for complex configurations that involve more than one mesh. Modules for two-stage and three-stage systems along with idler, planetary, star, and reverted gear train configurations have been developed. In complex gearbox systems, such as those in wind turbines, a sub-optimal split of the ratios in the gearbox can result in literally thousands of pounds of excess weight in the final design. Additionally, existing designs that are sub-optimal may benefit from the optimization process by re-specifying the diametral pitches and tooth counts in order to increase power capacity without adding additional weight. Optimizing for weight has the potential to squeeze precious pounds out of any existing system, including those in automotive and aircraft applications.
For those companies who have developed gear materials and processes that result in improved properties and wish for them to be incorporated into new customer designs, BCG-MinWeight can be used to justify their use by quantifying their benefits in terms of reduced size and weight. In the illustration above, three designs are shown, which utilize properties from AGMA Grades 1, 2, and 3 gear steels. All designs are specified to transmit 250 Hp through a single-stage reduction ratio of 2.5 with an input rotational speed of 2,000 rpm. For the three AGMA grades of steels using the carburization process, appropriate allowables for contact and bending stresses would be:
• Grade 1 – 180 ksi contact and 55 ksi bending
• Grade 2 – 225 ksi contact and 65 ksi bending
• Grade 3 – 275 ksi contact and 75 ksi bending
The results of the optimization process reveal the following:
• Grade 1 – center distance = 6.813”, estimated gear cylinder weights = 41.9 lbs
• Grade 2 – center distance = 5.500”, estimated gear cylinder weights = 29.5 lbs
• Grade 3 – center distance = 5.583”, estimated gear cylinder weights = 21.0 lbs
The results of this comparison indicate that the potential exists to reduce the overall weight of the specified design by 50 percent if the benefits of using a Grade 3 material vs. a Grade 1 material are fully utilized.
With more than 60 years of combined experience in the industry, BCGear & Engineering, Inc. provides solutions to development problems from concept to production.
For more information: bcgearengineering@gmail.com
