AGMA 16FTM13

The purpose of this paper is to show a method of designing and specifying gear teeth with much higher bending and surface contact strength (reduced bending and surface contact stresses). The primary means of achieving this is by specifying gear teeth with significantly higher pressure angles. This paper will show calculation procedures, mathematical solutions, and the theoretical background and equations to do this. For many gearing applications, maximizing gear tooth bending and surface contact strength is desired and essential. Any design that increases gear tooth bending and surface contact strength is a distinct advantage. Either the gears themselves or the assembled gearboxes can be made smaller, thinner, lighter, less expensive, or with higher torque rating and capacity, power density, and longer design life. It has been long known that higher pressure angle gears have strength advantages as well as some limitations compared to gears with normal pressure angles and more traditional designs. Some of the design considerations and limiting factors governing the design and specification of high pressure angle gears are: top land (tooth thickness at the O.D.) which can be thinner; contact ratio, which can be lower; minimum whole depth, which can be less; and hob tip radius and the resulting generated root fillet radius and tip to root clearance, which can be reduced from standard values. The required user input factors for the method described in this paper are: numbers of teeth, pinion and gear; diametral pitch; center distance; desired minimum top land, pinion and gear; desired contact ratio; and maximum backlash. The desired pressure angle can then be entered and another value re-entered to make comparisons. The output factors would be the outside diameters of the pinion and gear, and other gear data, based on the entered pressure angle. A convergence routine can calculate and match the pressure angle to the desired contact ratio. A spreadsheet or computer program can be created from the equations and formulas included in this paper to automate the mathematical calculations. The advantage of the methods described in this paper is that gear teeth of various different pressure angles can be calculated, compared, and evaluated quickly and easily, and high pressure angle gears can be designed and specified from simple and limited inputs. Gears can be designed based on desired top lands, contact ratio, and hob tip radius. An example in this paper will show a gear set with a pressure angle of 36 degrees with a sharp (zero) hob tip radius, a gear set with a 35-degree pressure angle, and a hob tip radius of 0.007 inch, and a gear set with a pressure angle of 33.5 degrees and a 0.020-inch hob tip radius. A reference design with a 25-degree pressure angle is also shown for comparison purposes.

In addition to the gear teeth top land considerations, a second parameter will be considered and calculated based on a user-specified hob tip radius.

In the past, higher pressure angle gears have not been commonly designed and specified because of the relative difficulties involved in designing them and the lack of appropriate and easy-to-use tools to evaluate them. This paper contributes to making it easier to accomplish this task.

Edition:

16#

Published:

09/01/2016

Number of Pages:

22

File Size:

1 file , 2.9 MB