Gear Sizing Project

The purpose of this project was to detail the design of three spur gears that would be suitable for a commercial three-gear train consisting of an input pinion, an idler gear, and an output gear. The pinion is required to mesh with the idler which in turn meshes with the output gear. The required gear ratio for the gear set is 3.5 to 1. The speed of the pinion shaft is 3000 rpm and must transmit 25 hp to the idler gear. The required service life is 5 years of one-shift operation. Also, the operating temperature of the gears in the gear train is 200. The design process is iterative and therefore many factors were considered to determine the final solution. The initial iteration has the following components:

  1. The diametrical pitch is P = 6 teeth/inch with a pressure angle of 20.
  2. The number of teeth on the pinion gear is 14 and the number of teeth on the idler is 17.
  3. The teeth are standard AGMA full depth profiles, ground, uncrowned, and the loads are uniform.
  4. The loads are applied at the highest point of single tooth contact and the quality number is 6.
  5. The pinion, the idler gear, and the output gear are Grade 1 – nitralloy steel with Poisson’s ratio of 0.28, a modulus of elasticity of 30 Mpsi, and a Brinell hardness number of 300.

Due to the iterative nature of this process, only one procedure was hand calculated. Further iterations were done in Matlab. What follows in the next section are the results from the first, second, third, and final iterations. It should be noted that the information shown above is only for the first iteration.

It 1

 

it 2

 

it 3

 

it 4

Shown above are the four iterations. These are the results from my Matlab program. As you can see, A lot of the results moved around to settle at reasonable factors of safety. I did not want any factor of safety below a 1.5. Therefore, the lowest is the wear on the pinion.

Face width

Shown above is a graph detailing how the factors of safety change with face width change. Clearly, face width increase proves a larger factor of safety. It is interesting to see how the different stresses change.